Chapter IV: NATURAL HISTORY.--Our Origin as a Species. By RICHARD (2)

From the foregoing it will be seen that, while presenting some advantages, the natural harbor of Vera Cruz possesses many drawbacks and dangers which the design of Mr. Eads will completely remove. The leading features of the works about to be carried out are indicated on the plan. They comprise

1. The construction of a sea wall between La Gallega and the Lavendera reefs, with an extension over the latter.

2. The construction of a sea wall from Punta de la Caleta to La Gallega. This part of the work will be begun after the completion of the first wall to a height of at least 3 ft. above low water.

3. A dike connecting the northern ends of the first two dikes with each other, and stretching across the southern part of La Gallega, to prevent the seas which sometimes break over this reef from entering the harbor. The wall between La Gallega and Lavendera will not only cut off the rough water during northerly gales, but will also effectually prevent the deposition of sand in the harbor, because the through passage to the northwest will be stopped. Passages closed by sluice gates will be formed through this wall at about low water level, so that at any time the harbor may be flushed out and stagnation prevented.

4. After the construction of the inclosing walls the harbor will be dredged out and cleared of coral to a depth of 25 ft. below low water.

5. Following these works of primary importance comes the construction of a wooden roadway from the Hornos reef to the northwestern dike. This roadway will form the south front of the harbor, and the excavated material will be deposited on the space between the roadway and the existing bottom, so as ultimately to make it a permanent work with a masonry retaining wall fronting the harbor. The land between the roadway and the city would also be reclaimed to the extent of more than 740,000 square yards.

6. The construction of wooden piers at right angles to the roadway, which would be extended to run around the harbor as trade required it, for ships to be alongside for loading and unloading. The construction of these short piers would be similar to those used in New York and other United States ports, and they might afterward be replaced by masonry if the increase in trade justified so large an expenditure.

7. The erection of a lighthouse, at or near the eastern end of the Lavendera sea wall of a second on the eastern side of La Gallaguilla reef, and of another on the west side of La Blanquilla reef. These houses will be furnished with distinctive signals to enable steamers running in before another to run with safety between La Gallaguilla and La Blanquilla as soon as the Lavendera light is seen between the other two.

The width of deep water at the entrance between the Lavendera and Hornos reefs will be 1,000 ft. The estimated cost of these extensive works is ten millions of dollars, a large sum for the Mexican Republic to expend in harbor improvements at one port but it will doubtless be found a profitable investment as it will tend greatly to promote trade, and so increase indefinitely the commerce of the port.

Mr. Eads' plan having been approved by the Mexican Government the work was formally commenced on the 14th of last August. Plans were also furnished by him at the request of the Government, for deepening the mouth of the Panuco River upon which is located the city of Tampico, the Gulf terminus of the Mexican central railway system.--_Engineering._

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COST OF POWER TO MAKE FLOUR.

The following estimate of the cost of the power required to manufacture a barrel of flour is taken from the _Miller_. The calculation would hardly hold good in this country owing to difference in cost of fuel attendance etc., but is nevertheless of interest.

"The cost of a steam motor per 20 stone (280 lb.) sack of flour depends entirely on local circumstances. It depends first, on the amount of power expended in the production of a sack of flour, that is on its mode of manufacture, and it depends, secondly, on the cost of the necessary amount of power, that is, on the cost of fuel burned per horse power The average consumption of coal of first class steam engines may be taken at 2 lb. per hour per indicated horse power.

"Supposing a mill with six pairs of stones, two pairs of porcelain roller mills, and the necessary dressing, purifying, and wheat cleaning machinery to require a steam motor of 100 indicated horse power to drive it, then the average consumption of fuel in this mill would be 200 lb. of coal per hour. Such a mill working day and night will turn out about 400 sacks of flour per week of, say, 130 hours, so that 200 X 13 = 26,000 lb. of coal would be required to manufacture 400 sacks of flour. The cost of this quantity of coal may be taken at, say, L12 (about $58.32), and for cost of attending engine and boiler, cost of oil, etc., another L3 (about $14.58) per week may be added; so that, in this case, the manufacture of 400 sacks of flour would cause an expenditure of L15 ($72.90) for the steam motor. Therefore the cost of the steam motor per 20-stone sack of flour may be taken at 9d. (about 18 cents) per sack, if an improved low grinding system is used.

"In this case it is supposed that about 55 per cent. of flour is obtained in the first run, leaving about 30 per cent. of middlings and about 12 per cent. of bran, which is finished in a bran duster. The middlings are purified, ground over one pair of middling stones, then dressed through a centrifugal and the tailings of the latter are passed over one of the porcelain roller mills, whereas the other porcelain roller mill treats the second quality of middlings coming from the purifier. The products from the two porcelain roller mills are dressed through a second centrifugal, and the whole flour is mixed into one straight grade. Four pairs of stones are supposed to work on wheat, one on middlings, and one pair is sharpening. The first run is supposed to be dressed through two long silk reels. Of course, not every steam motor has so low a consumption of coal as two pounds per hour per horse power; it often amounts to three, four, and five pounds per hour. In that case, of course, the cost of steam power per sack is much greater than 9d. per sack. A greater number of breaks does not necessarily increase the cost of steam power per sack of flour. Although more machines may be employed, each of them may require less horse power; so that the total amount of power required for manufacturing an equal amount of flour may not be greater in the case of gradual reduction.

"As, however, the cost of maintenance may be slightly greater in the latter case, on account of a greater number of more elaborate machines, the cost of manufacturing a sack of flour may be a little greater when gradual reduction is employed, taking into account the total expenses of the mill and interest on the capital employed.

"Water motors are generally a much cheaper source of energy than steam motors, but they are not so reliable and constant as the latter. The very irregular supply of water sometimes causes stoppages of the mill, and often a reserve steam engine has to be provided in order to assist the water motor when the quantity of water decreases during the summer months. Wind motors were formerly extensively used for milling purposes, but they are now gradually disappearing. They are too irregular and unreliable, although they utilize a very cheap motive power. It is not advantageous to expend a large amount of capital for a mill which often is unable to work at the very time when there are favorable opportunities for doing profitable business. Animal motors are too dear. They are only suitable for driving very small mills in out of the way localities."

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DRIVING GEAR MECHANISM FOR LIFT HAMMERS.

A very interesting system of driving gear for lift hammers was applied in an apparatus exhibited at Frankfort in 1881 by Mr. Meier of Herzen. The arrangement of the mechanism is shown in Figs. 1 and 2. In the upper part of the hammer-frame there is a shaft which is possessed of a continuous rotary motion, and, with it, there is connected by a friction coupling a drum that receives the belt from which is suspended the hammer. In the apparatus exhibited, the mechanism is so arranged that the hammer must always follow the motion of the controlling lever in the same direction; but a system may likewise be adopted such that the hammer shall continue to operate automatically, when and so long as a lever prepared for such purpose is lowered.

_ab_ is the shaft having a continuous rotary motion, and upon which are fixed the pulley, c, the fly-wheel, d, and the friction-disk, e. Upon one of the extremities of the driving shaft is fixed an elongated sleeve, formed of the drum, g, and of the screw, f, carried by the nut, h. This latter is supported in the frame in such a way that it cannot turn, but can move easily in the direction of the axis. Such motion may be produced by the spring, i, and its extent is such that the drum, g, is brought in contact with the friction-disk, e.

The hand-lever, k, rod, l, and bent lever, m, serve to bring about a motion in the opposite direction, and which disengages the drum, g, from the disk, e, and lets the hammer fall; the drum being then able to turn freely. If the lever, k, be afterward raised again, the spring, i, will act anew and couple the drum with the driving-shaft, so that the hammer will be lifted. In this rotary motion the screw, f, turns or re-enters into its nut, which it displaces toward the left, since it cannot itself move in that direction until the rectilinear motion be wiped out, and the power of the spring be thus overcome. At the same moment, the screw should naturally also make this rectilinear movement forward, that is to say, the coupling would be disengaged, if, at the least lateral motion toward the right, the spring, i, did not push the system toward the left. There is thus produced a state of equilibrium such that there is just enough friction between the disk, e, and the drum, g, to keep the hammer at rest and suspended. Through the action of an external force which lowers the lever, K, the hammer at once falls, and the screw issues anew from its nut and brings the parts into their former positions.

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DE JUNKER & RUH'S MACHINE FOR CUTTING ANNULAR WHEELS.

The machine shown in Figs. 1, 2, and 3 has been devised by Messrs. Junker & Ruh, of Carlsruhe, for cutting internally-toothed gear-wheels. The progress of the work is such that the wheel is pushed toward the tool by a piece, n, provided with a curve guide, and that the tool is raised and separated from the wheel after a tooth has been cut, in order to allow the wheel to revolve one division further.

The tool is placed in a support, b, which is fixed to the upright, d, in such away that it may revolve; and this support is connected to the frame, a, of the machine. A strong flat spring, f, constantly presses the tool-carrier, b, toward the upright, d, as much as the screw, g, will permit; and this pressure and the tension of the belt draw the tool downward. The screws, g, determine the depth of the cut, and compensate for the differences in the diameter of the tool.

The wheels to be cut are set by pressure into a wrought iron ring, with which they are placed in a sleeve or support, h. The connection between the two is assured by means of a nut, c. The axle of the support, h, is held in the upright of the carriage, k, which receives from a piece, l, placed on the driving-shaft, n, a slow forward motion toward the tool, and a rapid motion backward. The trajectory curve or groove of special form of the piece, l, in which moves the conducting roller, o, of the carriage, is not closed everywhere on the two sides, in that the guides that limit it extend only on the part strictly necessary. This arrangement permits of the roller being made to leave the trajectory in order that the carriage may be drawn back to a sufficient distance from the tool when the wheel is finished, so as to replace the latter by another.

One hollow is cut during each forward travel of the carriage; and, when such travel is finished, a cam-disk, p, placed on the shaft, n, lifts the tool-carrier, b, and thus draws the cutting-tool out of the hollow cut by it, so that the carriage cam can then move back without restraint. In the interim, the sleeve, h, which supports the wheel, revolves one tooth through the following arrangement: On the axis, e, of this sleeve there are two ratchet-wheels, r and s, the number of whose teeth is equal to that of the teeth to be cut in the wheel. The wheel, r, produces the rotation of the sleeve, h, and the wheel, s, keeps the shaft stationary during the operation. The two wheels are set in motion by a lever, t, or by its click, this lever being raised at the desired moment on the free extremity of the driving shaft, n, by a wedge, u. The short arm of the lever, t, engages, through its point of appropriate shape, with the teeth of the wheel, s, so as to keep this latter stationary while the tool is cutting out the interspace between the teeth. When the lever, t, is raised, this point is at first disengaged from the wheel, s; and the raising of the lever being prolonged, the button, i, places itself against the upper curve of the slot in the lever, q, and raises that likewise. q is connected with the lever, v, which revolves about the axis, e, and v carries the click, w, so that when the lever, v, is raised, the wheel, r, turns forward by one tooth. When the lever, t, is lowered, as the wedge, u, turns more, its click holds the wheel, s, stationary. This series of operations is repeated until the last interspace between the teeth has been cut, when the machine stops automatically as follows: A cam of the disk, A, which receives from the shaft, n, through cone-wheels, a motion corresponding to that of the wheels, r and s, abuts against the two-armed lever, z, and this latter then disengages the rod, y, so that the weight, G, can move the fork, B, in such a way that the belt shall pass from the fast to the loose pulley.

Motion is communicated to the machine as a whole by the shaft, C, which is provided with a fast and loose pulley. As shown in the engraving, the pulley, D, moves the tool, and the pulley, E, causes the revolution of the shaft, n, through a helicoidal gearing, F.

The construction of the tool carrier is represented in detail in Fig. 3. The cutting tool, F, rests on a sleeve forming part of the pulley, r1, against which it is pressed by a nut, while its position is fixed by a key. The axle, s1, of the tool is held in two boxes, in which it is fixed by screws. In order that the tool may be placed exactly in the axis of the wheel to be toothed, and that also the play produced by lateral wear of the pulley, r1, may be compensated for, two screws, r2, are arranged on the sides. All rotation of the shaft, s1, is prevented by a screw, o, which traverses the cast iron stirrup, C, and the steel axle box.

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RECENT HYDRAULIC EXPERIMENTS.

At a late meeting of the Institution of Civil Engineers, the paper read was on "Recent Hydraulic Experiments," by Major Allan Cunningham, R.E.

This paper was mainly a general account of some extensive experiments on the flow of water in the Ganges Canal, lasting over four years--1874-79. Their principal object was to find a good mode of discharge measurements for large canals, and to test existing formulae. There are about 50,000 velocity, and 600 surface-slope measurements, besides many special experiments. The Ganges Canal, from its great size, from the variety of its branches abounding in long straight reaches, and from the power of control over the water in it, was eminently suited for such experiments. An important feature was the great range of conditions, and, therefore, also of results obtained. Thus the chief work was done at thirteen sites in brickwork and in earth, some being rectangular and others trapezoidal, and varying from 193 ft. to 13 ft. in breadth, and from 11 ft. to 7 in. in depth, with surface-slopes from 480 to 24 per million, velocities from 7.7 ft. to 0.6 ft. per second, and discharges from 7,364 to 114 cubic feet per second. For all systematic velocity measurements, floats were exclusively used, viz., surface floats, double floats, and loaded rods. Their advantages and disadvantages had been fully discussed in the detailed treatise "Roorkee Hydraulic Experiments"--1881. They measured only "forward velocity," the practically useful part of the actual velocity. The motion of water, even when tranquil to the eye, was found to be technically "unsteady;" it was inferred that there is no definite velocity at any point, and that the velocity varies everywhere largely, both in direction and in magnitude. The average of, say, fifty forward velocity measurements at any one point was pretty constant, so that there must be probably average steady motion. Hence average forward velocity measurements would be the only ones of much practical use. To obtain these would be tedious and costly, and special arrangements would be required to obviate the effects of a change in the state of water, which often occurred in a long experiment, as when velocities at many points were wanted.

As to surface-slope its measurement--from nearly 600 trials--was found to be such a delicate operation that the result would be of doubtful utility. This would affect the application of all formulas into which it entered. The water surface was ascertained, on the average of its oscillations, to be sensibly level across, not convex, as supposed by some writers. There were 565 sets of vertical velocity measurements combined into forty-six series. The forty-six average curves were all very flat and convex down stream--except near an irregular bank--and were approximately parabolas with horizontal axes; the data determined the parameters only very roughly; the maximum velocity line was usually below the service, and sank in a rectangular channel, from the center outward down to about mid-depth near the banks. Its depression seemed not to depend on the depth, slope, velocity, or wind; probably the air itself, being a continuous source of surface retardation, would permanently depress the maximum velocity, while wind failed to effect this, owing to its short duration. On any vertical the mid-depth velocity was greater than the mean, and the bed velocity was the least. The details showed that the mid-depth velocity was nearly as variable from instant to instant as any other, instead of being nearly constant, as suggested by the Mississippi experimenters.

The measurement of the mean velocity past a vertical was thought to be of fundamental importance. Loaded rods seemed by far the best for both accuracy and convenience in depths under 15 ft. They should be immersed only 0.94 of the full depth. The chief objection to their use, that--from not dipping into the slack water near the bed--they moved too quickly, was thus for the first time removed. A double float with two similar sub-floats at depths of 0.211 and 0.789 of the full depth would also give this mean with more accuracy and convenience than any instrument of its class; this instrument is new. Measurement of the velocity at five eighths depth would also afford a fair approximation.

One hundred and fourteen average transverse velocity curves were prepared from 714 separate curves. These average curves were all very flat, and were convex down stream--over a level or concave bed--and nearly symmetric in a symmetric section. The velocity was greatest near the center, or deepest channel, decreased very slowly at first toward both banks, more rapidly with approach to the banks or with shallowing of the depth, very rapidly close to the banks, and was very small at the edges, possibly zero. The figure of the curve was found to be determined by the figure of the bed, a convexity in the bed producing a concavity in the curve and _vice versa_, and more markedly in shallow than in deep water. Curves on the same transversal, at the same site, and with similar conditions, but differing in general velocity, were nearly parallel projections. At the edges there was a strong transverse surface flow from the edge toward mid-channel, decreasing rapidly with distance from the edge. The discussion showed that it was almost hopeless to seek the geometric figure of the curves from mere experiment.

Five hundred and eighty-one cubic discharges were measured under very varied conditions. The process adopted contained three steps: (1) Sounding along about fifteen float courses, scattered across the site in eight cross sections; time, say four hours. (2) Measurement of the mean velocities through the full depths in those float courses, each thrice repeated; time, say four hours. (3) Computation, say two hours. This process was direct and wholly experimental; each step was done in a time which gave some chance of a constant state of water. From an extended comparison of all results under similar conditions, it appeared that the above process yielded, under favorable circumstances, results not likely to differ more than 5 per cent. The sequel showed that in a channel with variable regimen, a discharge table for a given site must be of at least double entry, as dependent on the local gauge-reading, and on the velocity or surface-slope.

Special attention was paid to rapid approximations to mean sectional velocity. The mean velocity past the central vertical, the central surface velocity, and Chezy's quasi-velocity--i.e.,

100 x Sqrt (R x S)

where R = the hydraulic mean depth, and S = surface slope--were tried in detail; thus 100, 76, and 83 average values thereof respectively were taken from 581, 313, and 363 detail values. The ratios of these three velocities to the mean velocity were taken out, and compared in detail with Bazin's and Cutter's coefficients. Other formulae were contrasted also in slight detail. Kutter's alone seemed to be of general applicability; when the surface slope measurement is good, and the rugosity coefficient known for the site--both doubtful matters--it would probably give results within 71/2 per cent. of error. Improvement in formulae could at present be obtained only by increased complexity, and the tentative research would be excessively laborious. Now the first two ratios varied far less than the third; thus their use would probably involve less error than the third, or approximation would be more likely from direct velocity measurement than from any use of surface slope. The connection between velocities was probably a closer one than between velocity and slope; the former being perhaps only a geometric, and the latter a physical one. The mean velocity past the central vertical was recommended for use, as not being affected by wind; the reduction coefficient could at present only be found by special experiment for each site. Three current meters were tried for some time with a special lift, contrived to grip the meter firmly parallel to the current axis, so as to register only forward velocity, and with a nearly rigid gearing wire. No useful general results were obtained. Ninety specimens of silt were collected, but no connection could be traced between silt and velocity; it seemed that the silt at any point varied greatly from instant to instant, and that the quantity depended not on the mean velocity, but probably on the silt in the supply water. Forty measurements of the evaporation from the canal surface were made in a floating pan, during twenty five months. The average daily evaporation was only about 1/10 in. The smallness of this result seemed to be due to the coldness of the water--only 63 deg. in May, with 165 deg. in the sun and 105 deg. in shade. Lastly, it must suffice to say that great care was taken to insure accuracy in both fieldwork and computation.

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THE GERM.

By ARTHUR ATKINS.

There seems to have sprung up within a few mouths a tendency to revive the discussion on that hackneyed question, "Shall the germ be retained in the flour?" This question has been more than once answered in the negative by both scientific and practical men, but recently certain prominent persons have come to the conclusion that every one has been wrong on this point, and the miller should by all means retain the germ. Now the nutritive value of the germ cannot be disputed, but there are two circumstances which condemn it us an ingredient of flour. The first is that the albuminoids which it contains are largely soluble, and this means that good light bread from germy flour is impossible. I have not time to go into a detailed explanation of the chemical reasons for this, but they may be found in a series of articles which appeared in _The Milling World_ about a year ago. In the next place, the oil contained in the germ not only discolors the flour, but seriously interferes with its keeping qualities. Now color is only a matter of taste, and if that were the only objection to the germ, it might be admitted, but we certainly do not want anything in our flour to interfere with making light, sweet bread, and will render it more liable to spoil. If our scientists can discover some method of obviating these objections, it will then be time enough to talk about retaining the germ. Meanwhile millers know that germy flour is low priced flour, and they are not very likely to reduce their profits by retaining the germ.--_Milling World._

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WHEAT TESTS.

There was considerable complaint last season, on the part of wheat raisers in sections tributary to Minneapolis, on account of the rigid standard of grading adopted by the millers of that city. It was asserted that the differentiation of prices between the grades was unjustly great and out of proportion to the actual difference of value. In order to ascertain whether this was the case or not, the Farmers' Association of Blue Earth County, Minn., decided to have samples of each grade analyzed by a competent chemist in order to determine their relative value. Accordingly specimens were secured, certified to by the agent of the Millers' Association of Minneapolis, and sent to the University of Minnesota for analysis. The analysis was conducted by Prof. Wm. A. Noyes, Ph.D., an experienced chemist, who has recently reported as follows:

"The analyses of wheat given below were undertaken for the purpose of determining whether the millers' grades of wheat correspond to an actual difference in the chemical character of the wheat. For this purpose samples of wheat were secured, which were inspected and certified to by M. W. Trexa on April 13th of this year. The inspection cards contained no statement except the grade of the wheat and the weight per bushel, but the samples were all of Fife, for the purpose of a better comparison. The analyses of the wheat were made during October in this laboratory. In each case the wheat was carefully separated from any foreign substances before analysis. The results of analysis were as follows:

Grade Grade Grade
No. 1. No. 2. No. 3.
Weight per bushel.................. 59 lb. 561/2 lb. 55 lb.
Grains to weigh 10 grains.......... 366 474 491
Per ct. Per ct. Per ct.
Foreign matter (seeds, etc.)....... 0.41 0.20 1.57
Nitrogen........................... 2.09 2.08 2.17
Phosphorus......................... 0.35 0.46 0.46
Water.............................. 12.34 11.31 11.85
Ash................................ 1.59 1.92 1.97
Albuminoids (nitrogen multiplied
by 61/4)........................... 13.06 13.00 13.56
Cellulose.......................... 2.03 2.37 2.50
Starch, sugar, fat, etc............ 70.98 71.40 70.12

"The analyses require but little comment. The only substances in which there is evident connection between the results of analysis and the grades of wheat are the cellulose, ash, and phosphorus. As regards the last substance, grades two and three seem to have the greatest food value. But it seems quite probable from the results that greater difference would be found between different varieties of wheat of the same kind than is shown here between different grades of the same variety of wheat. However, it does not necessarily follow from this that the different grades of wheat are of nearly equal value to the miller for the purpose of making flour. That is a question which can be best answered by determining accurately the amount and character of the flour which can be made from each grade of wheat. If possible, the investigation will be continued in that direction."

As Prof. Noyes justly remarks, the value of the different grades of wheat can best be determined by a comparison of the results of reducing them to flour, but an intelligent study of the table given above would of itself be sufficient to indicate the justness of the grading. In the first place, even were the percentages of the different components exactly the same in each grade, still the difference in weight would of itself be sufficient to justify a marked difference in price. This requires no proof, for, other things being equal, fifty-nine pounds is worth more than fifty-five pounds. Again, the figures show that No. 3 contained nearly four times as much foreign matter as No. 1. Millers certainly should not be expected to pay for foreign seeds or other substances valueless for their purpose, at the price of wheat. Finally, if the analysis proves anything, it proves that the lower grades contain a decidedly larger percentage of components which it is generally agreed, whether directly or the reverse, ought not to be incorporated with the flour, and are, therefore, of comparatively little value to the miller. This is shown by the relative amounts of cellulose, ash, and phosphorus present. Cellulose, as every one knows, is the woody, indigestible substance which is found in the bran, and the greater the amount of cellulose, the heavier will be the bran in proportion to the flour producing elements. According to the figures presented, No. 3 contained nearly one-quarter more cellulose than No. 1, while the amount in No. 2 was slightly less than in No. 3. The ash, too, which represents the mineral constituents of the wheat, is directly dependent upon the quantity of bran. Here, too, the lowest grade is shown to yield about one-quarter more than the highest. The larger percentage of phosphorus in the lower grades is suggested by the analyst to indicate their greater food value in this respect. So it would, were we in the habit of boiling our wheat and heating it whole, or of using "whole wheat meal." But, fortunately or unfortunately, the bread reformers have not yet succeeded in inoculating any considerable portion of the community with their doctrines, and hence the actual food value of any sample of wheat must be ascertained, not directly from the composition of the wheat, but from the composition of the flour made therefrom. Now, as already stated, phosphorus, like the other mineral components, is found almost entirely in the bran. Its presence in greater quantity, therefore, simply adds to the testimony that a larger proportion of the low grade wheat must be rejected than of the higher grade. It should be evident to the complaining farmers that the millers were in the right of the question, on this occasion at least.

It is expected that further analysis will be made, this time of the flour made from the different grades of wheat. If these investigations be properly conducted, we have no doubt that they will simply confirm the evidence of the wheat tests. A chemical analysis alone, however, will not be sufficient. The quantity of flour obtained from a given amount of wheat must also be ascertained and its quality further tested by means best known to millers, as regards "doughing-up," keeping qualities, color, etc. And then the result can be no less than to show what millers already knew--that the best quality of flour, commanding the top prices in the market, cannot be obtained from an inferior quality of wheat.--_Milling World._

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APPARATUS FOR PRINTING BY THE BLUE PROCESS.[1]

[Footnote 1: Read June 21, 1882, before the Boston Society of
Civil Engineers.]

By CHANNING WHITAKER.

The blue process is well known to the members of the society, and I need not take time to describe it; but with the ordinary blue process printing frame the results are sometimes unsatisfactory, and now that the process has come to be so commonly used I have thought that an account of an inexpensive but efficient printing frame would be of interest. The essential parts of the apparatus are its frame, its glass, its pad or cushion, its clamps, and the mechanism by which the surface of the glass can easily be made to take a position that is square with the direction of the sun's rays.

_The Blue Process Printing Frame in Common Use.--Its Defects._--The pad of the apparatus in common use consists of several thicknesses of blanketing stretched upon a back board. The sensitized paper and the negative are placed between the pad and the plate glass, and the whole is squeezed together by pressure applied at the periphery of the glass and of the back-board. Both the glass and the back-board spring under the pressure, and it results that the sensitized paper is not so severely pressed against the negative near the center of the glass as it is near the edges. If at any point the sensitized paper is not pressed hard up against the negative, a bluish tinge will appear where a white line or surface was expected. With an efficient printing frame and suitable negatives, these blue lines will never appear, and it was to prevent the production of defective work that I undertook to improve the pad of the printing frame.

_The Printing Frame Used in Ordinary Photography._--Very naturally, I first examined the printing frame used in ordinary photography. This frame is extremely simple, and is very well adapted to its use. It is, undoubtedly, the best frame for blue process printing, when the area of the glass is not too large. The glass is set in an ordinary wooden frame, while the back-board is stiff and divided into two parts. A flat, bow-shaped spring is attached by a pivot to the center of each half of the back-board. The two halves of the back-board are hinged together by ordinary butts. Four lugs are fastened to the back of the frame, and, when the back-board is placed in position, the springs may be swung around, parallel to the line of the hinges, and pressed under the lugs, so that the back of the back-board is pressed most severely at the center of each half, while the glass is prevented from springing away from the back-board by the resistance of the frame at its edges. Unless the frame is remarkably stiff, it will resist the springing of the glass more perfectly in the neighborhood of the lugs than elsewhere. It will now be seen that, on account of the manner in which the pressure is applied, the back-board tends to become convex toward the glass, while the adjacent surface of the glass tends to become concave toward the back-board; and that with such a frame, the pressure upon all parts of the sensitized paper is more nearly uniform than when the pressure is applied in the manner before described. With a small frame of this description, a piece of ordinary cotton flannel is used between the back-board and the sensitized paper, and, with larger sizes, one or more thicknesses of elastic woolen blanket are substituted for the cotton flannel. There is an advantage in having a hinged back-board like that which has been described, because, when the operator thinks that the exposure to sunlight has been sufficiently prolonged, he can turn down either half of the back and examine the sensitized paper, to see if the process has been carried far enough. If it has not, the back-board can be replaced, and the exposure continued, without any displacement of the sensitized paper with respect to the negative. This is an important advantage.

_An Efficient Blue Process Frame, for Printing from Large Negatives, or for Printing Simultaneously from many Small Ones._--In order to be efficient, such a frame must be capable of keeping the sensitized paper _everywhere tightly pressed against the negative_. Again, such a frame, being large, is necessarily somewhat heavy. It should be so mounted that it can be handled with ease; and, in order that it may print quickly, it should be so arranged that it can be turned without delay, at any time, into a position that is square with the direction of the sun's rays.

Undoubtedly, if a sufficiently thick plate of glass should be used, the ordinary photographic printing frames would answer the purpose, whatever the size, but very thick plate glass is both heavy and expensive. Commercial plate glass varies in thickness from one-fourth to three eighths of an inch, and the thicker plates are rather rare. A large plate of it is easily broken by a slight uniformly distributed pressure. But the pressure that is required for the blue process printing, although slight, is much greater than is used in the ordinary photographic process. For the sensitized paper that is used in the blue process printing is, comparatively, very thick and stiff, and it may cockle more or less, while the paper that is used in ordinary photography is thin and does not cockle. Now, it is easy to see that a pressure severe enough to flatten all cockles must be had at every part of the sensitized paper, and that, if the comparatively thin, inexpensive, light weight, commercial plate glass is to be used, it is desirable to have the pressure _nowhere much greater than is needed for that purpose_, lest the fragile glass should be fractured by it. In each of my large frames I use the commercial plate glass; instead of the cushion of cotton flannel, or of flannel, I use a cushion filled with air of sufficiently high pressure to flatten all cockles, and to press all parts of the sensitized paper closely against the negative; and instead of the hinged back-board I use a back-board made in one piece and clamped to the frame of the glass at its edges. Connected with the cushion is a pressure gauge, and a tube with a cock, for charging the cushion with air from the lungs. Experience shows what pressure is necessary with any given paper, and the gauge enables one to know that the pressure is neither deficient nor in excess of that which is safe for the glass.

_The Construction of the Air-Cushion._--The expense of such an air-cushion seemed at first likely to prevent its being used; but a method of construction suggested itself, the expense of which proved to be very slight. The wooden back-board, as constructed, is made in one piece containing no wide cracks. It has laid upon it some thick brown Manila paper, the upper surface of which has been previously shellacked to make it entirely air-tight. Upon this shellacked surface is laid a single thickness of thin paper of any kind; even newspaper will answer. Its object is simply to prevent the sheet rubber, which forms the top of the air-cushion, from sticking to the shellacked paper. The heat of the sun is often sufficient to bring the shellac to a sticky state. It would probably answer as well to shellac the under side of the paper, and to use but one sheet, but I have not tried this plan. Around the periphery of the pad, there is laid a piece of rubber gasket about one and a half inches wide, and about one-eighth of an inch thick. In order that the gasket may not be too expensive, it is cut from two strips about three inches wide. One of them is as long as the outside length of the frame, and the other is as long as the outside width of the frame. Each of these strips is cut into two L-shaped pieces, an inch and a half in width, with the shorter leg of each L three inches long. When the four pieces are put together a scarf joint is made near each corner, having an inch and one-half lap. It is somewhat difficult to cut such a scarf joint as perfectly as one would wish, and it is best to use rubber cement at the joints. Over the gasket is laid a sheet of the thinnest grade of what is called pure rubber or elastic gum. Above this, and over the gasket, is placed a single thickness of cotton cloth, of the same dimensions as the gasket, and yet above this are strips of ordinary strap iron, an inch and a half wide and nearly one eighth of an inch thick. These strips are filed square at the ends and butt against each other at right angles. As the edges of the strips are slightly rounded, they are filed away sufficiently to form good joints wherever the others butt against them. The whole combination is bound together by ordinary stove bolts, one quarter of an inch in diameter, placed near the center of the width of the iron strips, and at a distance apart of about two and one-half inches. Their heads are countersunk into the strap iron. In making the holes for the stove bolts through the thin rubber, care should be taken to make them sufficiently large to enable the bolt to pass through without touching the rubber, otherwise the rubber may cling to the bolts, and if they are turned in their holes the rubber may be torn near the bolts and made to leak. A rough washer, under each nut, prevents it from cutting into the back-board. For the purpose of introducing air to, or removing air from, the pad, a three-eighths of an inch lock nut nipple is introduced through the back-board, the shellacked paper, and its thin paper covering. Without the back-board a T connects with the nipple. One of its branches leads, by a rubber tube, to the pressure gauge, which is a U-tube of glass containing mercury. The other branch has upon it an ordinary plug cock, and, beyond this, a rubber tube terminating in a glass mouth-piece. When it is desired to inflate the air-cushion, it is only necessary to blow into the mouth-piece. A pressure of one inch of mercury is sufficient for any work that I have yet undertaken. With particularly good paper, a lower pressure is sufficient. Upon the top of the pad is laid a piece of common cotton flannel with the nap outward, and with its edges tacked along the under edge of the back-board. The cotton flannel is not drawn tight across the top of the pad. The reason for employing a cotton flannel covering is this: When the sheet rubber has been exposed for a few days to the strong sunlight, it loses its strength and becomes worthless. The cotton flannel is a protection against the destruction of the rubber by the sunlight. I first observed this destruction while experimenting with a cheap and convenient form of gauge. I used, as an inexpensive gauge, an ordinary toy balloon, and I could tell, with sufficient accuracy, how much pressure I had applied, by the swelling of the balloon. This balloon ruptured from some unknown cause, and I made a substitute for it out of a round sheet of thin flat rubber, gathered all around the circumference. I made holes about one-quarter of an inch apart, and passing a string in and out drew it tight upon the outside of a piece of three eighths of an inch pipe, I then wound a string tightly over the rubber, on the pipe, and found the whole to be air-tight. This served me for some time, but one day, on applying the pressure, I found a hole in the balloon which looked as if it had been cut with a very sharp knife. That it had been so cut was not to be imagined, and on further examination I found that the fracture had occured at a line which separated a surface in the strong sunlight from a surface in the shade, at a fold in the rubber. I saw that all of the rubber which had been continuously exposed to the intense sunlight had changed color and had become whiter than before, and that that portion of the balloon had lost its strength. I then returned to the use of the mercury gauge, and took the precaution to cover my pad with cotton flannel, as a protection from the light and from other sources of destruction. This pad is upon the roof of the Institute; and is exposed to all weathers. As a protection from the rain and the snow, the whole is covered again with a rubber blanket. It has withstood the exposure perfectly well for a year, without injury. The gauge, made from flat rubber, is altogether so cheap and so convenient that I am now experimenting with one of this description having a black cloth covering upon the outside. The balloon is of spherical shape, the black cloth covering is of cylindrical shape, and I hope that this device will serve every necessary purpose. A sectional view of the air-cushion is offered as a part of this communication.

_The Frame, which Contains the Plate Glass_, is made of thick board or plank, with the broad side of the board at right angles to the surface of the glass. A rabbet is made for the reception of the glass, and four strips of strap iron, overlapping both the glass, and the wood, and screwed to the wood, keep the glass in position. Strips of rubber are interposed between the glass and the wood and between the glass and the iron. The frame is hinged to the back-board by separable hinges, so that the glass can be unhinged from the pad without removing the screws. Hooks, such as are used for foundry flasks, connect the frame with the pad upon the opposite side. A frame made in this manner is very stiff and springs but little, and its depth serves an excellent purpose. The air-cushion and the frame are so mounted that they can be easily turned to make the surface of the glass square with the direction of the sun's rays. It is necessary to have a tell tale connected with the apparatus, which will show when the surface of the glass has been thus adjusted. The shadow of the deep frame is an inexpensive tell-tale, and enables the operator to know when the adjustment is right. I have now described, in detail, the construction of the air-cushion with its back-board, as well as that of the frame which holds the plate glass, and I think it will be evident that the first cost of the materials of which they are made is comparatively little, and that the workmanship required to produce it is reduced to a minimum. It will also, I think, be evident that a uniform pressure, of any desired intensity, can be had all over the surface of the sensitized paper for the purpose of securing perfect contact between it and the negative. The blue copies that are taken with this apparatus are entirely free from blue lines when the negatives, chemicals, and paper are good.

_The Mechanism for Adjusting the Surface of the Glass, until it shall be Perpendicular to the Direction of the Sun's Rays._--I have found many uses for the blue copying process in connection with the work of instruction at the Massachusetts Institute of Technology. Notes printed by it are far better and less costly than those printed by papyrograph. I will not detain you now with an account of the uses that I have made of it. I will merely say that more than a year ago I found that my frame, which has a glass 3 feet x 4 feet, was wholly inadequate to the work in hand, and I tried to increase the production from it by diminishing the time of printing. The glass of this frame was horizontal, except when one of its ends was tilted off from the slides which guided it when pushed out of the window; and I knew that it took three or four times as long to print when the sun was low as it did when the sun was near the meridian. I made plans for mounting this frame upon a single axis, about which it could be turned after it had been pushed through the window, but I saw that no movement about a single axis would give a satisfactory adjustment for all times of the year, and I considered what arrangement of two axes would permit a rapid and perfect adjustment, at all times, with the least trouble to the operator. It was evident that when the sun was in the equatorial plane, the surface of the glass should contain a line which was parallel to the axis of the earth; and further, that if such a glass was firmly attached to an axis which was parallel to that of the earth, it would fulfill the desired purpose. For the glass, being once in adjustment, is only thrown out of position by the rotation of the earth, and if the glass is rotated sufficiently about its own axis, in a direction opposite to that of the earth, it will retain its adjustment. In order to have the adjustment equally good when the sun was either north or south of the equatorial plane, it was sufficient to mount a secondary axis upon the primary one and at right angles to it. About this the glass could be turned through an angle of 231/2 deg., either way, from the position which it should have when the sun was in the equatorial plane.

_The Construction of the Adjusting Mechanism._--I desired to have the mechanism as compact and inexpensive as possible, and to have the frame well balanced about the primary axis, in every position. I also desired to have a rotation of nearly 180 deg. about the principal axis. The plan adopted will be most easily understood by referring to the drawing which illustrates it. The axes are composed chiefly of wood. They are built up from strips which are 3 inches x 7/8 inch, and from small pieces of 2 inch plank. They are stiffly braced. A pair of ordinary hinges permit the secondary rotation to occur, while a pair of cast iron dowel pins with their sockets, such as are used in foundry flasks, serve as pivots during the primary rotation.

_The Adjustments._--The adjustment about the secondary axis does not need to be made more frequently than once a week, or once a fortnight. In order to prevent rotation about this axis when in adjustment, two cords lead from points which are beneath the back board, and as far removed from the secondary axis as is convenient. Each cord passes forward and backward through four parallel holes in a wooden block which is attached to the primary axis. The cords can be easily slipped in the holes by pulling their loops, but the friction is so great that they cannot be slipped by pulling at either end. It takes about twice as long to make the adjustment as would be necessary if a more expensive device had been used; but this device is at once so cheap, so secure, and has so seldom to be used, that it was thought to be best adapted for the purpose. To prevent rotation from occurring about the primary axis when it is not desired, a bar parallel to the secondary axis is attached by its middle point to the primary axis near one end. A cord passes from either end of this bar through cam shaped clamps, which were originally designed for clamping the cords of curtains with spring fixtures. These clamps are cheap. They are easily and quickly adjusted, and are very secure.