Chapter III: Part 3

We have recorded the progress of improvement in the manufacture of glass, and now, relevant to the subject, we propose to examine the various improvements in working furnaces and glass-houses. To this end we present to our readers the drawing of a furnace for flint-glass,[1] with the interior of a glass-house as used by the Venetians, at the highest point of the art, in the sixteenth century.

[1] See drawing No. 1, at end of book.

The workmen in glass will see, that, as compared with the factories of the present day, the Venetians in their instrumentalities were subjected to many difficulties,--they were oppressed by the furnace smoke, and in no way protected from the heat of the furnace, or enabled to breathe fresh atmospheric air; in fact, the impression prevailed in those days that the external air, drawn into the glass-house, was detrimental to the business, and therefore it was most cautiously guarded against.

The drawing is taken from an ancient work on glass, and although limited in the view, shows the general plan. The factory wall was conical, and rose like a large chimney, with a few windows for the admission of light. Exposed to the heat of the summer sun of Venice, and of the furnace within, neither the comfort nor health of the workman was secured. The construction of the annealing department shows two tiers of pans, the use of which must have been attended with great loss of materials. Yet, with all the perceptible inconvenience, no material change in construction was made for centuries. The same plan was adopted in France and England, and it is only within the present century that any change has taken place in the latter country. In fact, in the year 1827 an Englishman erected a glass factory on the same plan in the vicinity of New York, which, from its defective construction for this climate, soon passed out of use.

The Germans, however, departed from the Venetian plan so far as to place the furnace in a large and well-ventilated building, but without a furnace-cone to carry off the heat and smoke; still a decided improvement was thus effected over the system in use in France and England.

The plan referred to shows to the practical workmen of the present day the excessive waste of fuel arising from the construction of the furnace; for the same expenditure of fuel in the American furnace would melt ten times the material produced from the Venetian.

It is admitted that the American glass-house is far in advance of the European ones at the present day, in the particulars of capacity, ventilation, comfort of the workmen, and economy in fuel. An impression is very prevalent that glass-making is an unhealthy occupation. It may have been thus in former times; but, as a matter of fact, no mechanical employment is more healthy. Dissipated as glass-makers have been in former days, and careless of their health as they are at present, no better evidence can be adduced to prove the _generally_ healthy character of the employment than the fact that the Glass Manufacturing Company in Sandwich, averaging in their employment three hundred hands, had not a man sick through the influence of the employment, or one die in their connection, for the space of twenty years.

Drawing No. 2[2] represents the plan adopted in the French flint-glass furnaces. These at one period were worked by noblemen only,--the labor of the furnace-tender and taker-in being performed by servants, as before stated. The apparel and general style of dress, as indicated by the drawing, shows that more attention was paid to the fashion of the day than to comfort. The form of the furnace being similar to the Venetian shows it to have been subject to the same unnecessary waste of fuel; but it would appear that the French manufacturers had taken one step towards improvement, in using the waste fuel of the furnace to anneal their glass. The Venetians had a separate furnace to anneal their glass, supported by independent fires, as used at the present day.

[2] See drawing No. 2, at end of book.

The place marked D, over the crown of the furnace, is the door of the annealing oven; but the drawing is so imperfect that the artist does not show by what flues the smoke escapes, or in what way the glass was drawn from the annealing oven; for only the external view of the furnace is given. But it is fair to presume that the plan was the same as still exists in France, and as adopted by a French company now working a flint-glass factory in Williamsburg, near New York; viz.,--the taker-in, so called, mounts by steps to door D and places the articles in iron pans, which are slowly drawn over the furnace and through another door on the opposite side, to allow the glass vessels to cool gradually. The use of this plan is sustained by writers who describe the tools used to carry the glass articles into the upper oven to cool. In connection with the drawings of the ancient glass-furnaces, we deem it proper to give a drawing of glass-makers' tools[3] in use at that period, so that the glass-makers of the present day may observe with what instruments their noble predecessors in the art performed their labor.

[3] See drawing No. 3, at end of book.

In many of these tools we perceive the same general characters as mark those in use now. In some, improvements have been effected; while others are quite obsolete. It is quite curious to observe the etymology of many of the technical terms of the art in use at the present day. The name of the present polished iron table, _i.e._ the MARVER, is derived from the practice of the Italians and French in using slabs of polished marble. The iron now called the _punty_, from the Italian _ponteglo_. The tool now called _percellas_, from the word _porcello_. In fact, nearly all the technical terms in the glass manufacture, appertaining to the tool or furnace, are derived from the Italian. By referring to the drawing, we see that the tool marked A is the blow-iron, that marked B the punty-iron. Their character plainly indicates that the work made on them must have been confined to small or light articles. C, the scissors, D, the shears, correspond to those used at the present day. The tool marked E was used to finish part of their work. F and G were their large and small ladles,--the small used to take off the then called alkalic salt, showing that they were troubled with an excess of this in their time. The shovel, then called stockle, marked H, was used to carry glass articles to the annealing oven, forks not being then in use. The crooked iron I was used to stir up the metal in the pots. The tool L was used to form or hold large articles, their punty-iron not having sufficient strength. The tool M was used to carry flat articles to the annealing ovens. The tool N was used in refining their alkalic salts, and served to take off the salt as crystallized in course of its manufacture.

The workmen of the present day will see that, as before remarked, many tools are not altered in form, while in others there is a decided improvement,--in none more than in the tool E. Tool D is exactly like those now in use; but many new tools have been introduced since that period, rendering most of the old tools useless. Improvements in the form of glass-furnaces, construction of the glass-house, tools, &c., have been very gradual,--more so, in fact, than in almost any other art, when we consider that a period of about four hundred years has elapsed since the furnaces, tools, &c., herein referred to, were in use, and that they remained very much the same until the present century. It is indeed no undue arrogance of claim to say that the very many improvements in furnaces, working machinery, tools, &c. (such as enable the manufacturer here to melt with the same fuel double the quantity of glass that can at present be done in the European furnaces,) are entirely owing to the progress of the art in this country. By the perfection of our machines double the product can be obtained; and although the glass maker is paid at least three times the wages usually paid in Germany or France, we can, in all the articles where the value of the materials predominates, compete successfully with importers of foreign glass; but when the labor on glass constitutes its chief value, then glass can be imported cheaper than it can be manufactured in this country. Essentially, however, we may say, in the realm of art as in that of civilization and progress,--

"Westward the star of empire takes its way."

PRESSED GLASS.

This important branch of glass-making demands more than a passing notice. Although it is commonly believed here that the invention originated in this country, the claim cannot be fully sustained. Fifty years back the writer imported from Holland salts made by being pressed in metallic moulds, and from England glass candlesticks and table centre-bowls, plain, with pressed square feet, rudely made, somewhat after the present mode of moulding glass. From 1814 to 1838, no improvement was made in Europe in this process, which was confined to common salts and square feet.

America can claim the credit of great improvements in the needful machinery which has advanced the art to its present perfection. More than three quarters of the weekly melt is now worked up into pressed glass, and it is estimated that upwards of two million dollars has been expended in the moulds and machines now used in this particular branch of glass-making. This leaves Europe far behind us in this respect. With us there is active competition for excellence. It is, however, conceded that James B. Lyon & Co., of Pittsburg, stand first. To such a degree of delicacy and fineness have they carried their manufacture, that only experts in the trade can distinguish between their straw stem wines, and other light and beautiful articles made in moulds, and those blown by the most skilled workmen. When we consider the difference in the cost between pressed and blown ware, this rivalry in beauty of the former with the latter becomes all the more important to the public, as it cheapens one of the staple necessaries of civilized life.

Great credit therefore is due this firm for their success in overcoming difficulties well understood by glass-makers, and doing away with the prejudice of the skilled blowers, who naturally were not inclined to put the new and more mechanical process of manufacturing glass on a par with the handicraft of the old. Lyon & Co. also excel all other American firms in large ware for table services, as well as in the more delicate objects of use.

In speaking of the improvements in glass-making in America, we must not overlook what has been done by the New England Glass Company.

Convinced of the importance of scientific skill in their business, they secured some years ago the services of Mr. Leighton and his three sons, at a liberal compensation. Besides possessing the best practical knowledge, they had also artistic taste, which enabled them to give elegant finish to their workmanship, and to introduce new and more beautiful patterns into it.

They did not neglect, however, the more homely but useful articles; but executed orders for large and heavy objects for druggists' and chemical wares and philosophical apparatus, so satisfactorily as to secure a monopoly in them. Their richly cut, gilded, colored, and ornamental glass is considered equal to European work.

John L. Gillerland, late of the Brooklyn Glass-Works, is remarkably skilful in mixing metal. He has succeeded in producing the most brilliant glass of refractory power, which is so difficult to obtain. A gold medal was awarded his glass, in face of European competition, at the Great International Exhibition in London, 1852. In making rich glass, the gaffer or foreman must understand the science of chemistry sufficiently well to mix and purify his materials in the best possible manner, removing all crude or foreign matter, and combining the proper substances into a homogeneous mass. Without this practical experience and knowledge, his glass, instead of being clear and brilliant, and of uniform color, will be dull, and of many hues or shades. It is important also that his personal character be such as to command the respect of the workmen.

LENSES.

Optical glasses have engaged the attention and investigation of scientific men for centuries. We read of the wonderful exploits of the burning lens of Archimedes, and find the remains of lenses thousands of years old in the ruins of Nineveh, Babylon, and Pompeii. They are of the utmost importance in the science of astronomy. The slow progress made in perfecting them shows the inherent difficulties that exist in obtaining glass of the required purity. One of these is the different specific gravities of the material used. Hence the lower part of a pot of melted glass is of greater specific gravity than the top, causing a tendency to cords or threads, an evil which science has yet to learn to overcome. Not even the large bounty offered by the English Government and the Board of Longitude has been successful in effecting any important improvement in this branch of manufacture. Munich enjoys the reputation of producing the best lenses, and consequently the finest telescopes. Sir Isaac Newton, Gregory, Dolland, Keir, and others adopted lenses made from flint- and from crown-glass, it being necessary to use both in the construction of achromatic telescopes, one possessing as small and the other as great dispersive powers relative to the mean refractive powers as can be procured. But the inherent defect of the lenses still remained. M. Macquer remarks, "The correction of this fault appears therefore to be very difficult." He had tried in vain to remove it by very long fusion and fierce fire. Others have found this by experience not to correct, but to augment the evil. Mr. Keir is of opinion that some new composition must be discovered, which, along with a sufficient refractive power, shall possess a greater uniformity of texture.

Since then, it is certain some improvement has been made in the composition for lenses. In an English paper we find the following:--"One of the most remarkable optical lenses of modern manufacture is that produced by Messrs. Chance, English manufacturers, being an attempt by them to improve the manufacture of glass for optical purposes. The diameter is twenty-nine inches, and it is two inches and a quarter thick. It is really not a lens, but a plain disk intended for a lens, should its quality be sufficiently fine. The weight is about two hundred pounds. This piece of glass was inspected, on its first public exhibition, by eminent scientific judges. It was by them examined edgewise, transversely, and obliquely; it was viewed by daylight and by candle-light; it was tested by the polariscope and by other means; and after having been thus subjected to a severe ordeal, it was pronounced to be the largest and finest known specimen of the kind."

The promise held out by the foregoing we fear has failed, as in very many previous cases, or the world ere this time would have heard of its success. An achromatic object-glass for telescopes consists of at least two lenses, the one made of flint-glass, and the other of crown-glass. The former, possessing least power of dispersing the colored rays relative to its mean refractive power, must be of greater value than the latter. It is upon this principle that the achromatism of the image is produced, the different colored rays being united into one focus. Flint-glass, to be fit for this delicate purpose, must be perfectly homogeneous, of uniform density throughout its substance, and free from wavy veins or cords.

From the foregoing, the reader will see that, as has been said, the chief difficulty which exists in making telescopic lenses arises from want of pure glass. Every attempt to correct this evil has failed; it is well known our best telescopes and like optical instruments have always achromatic lenses, and for photographic purposes achromatic lenses are indispensable. If philosophers and astronomers have with so imperfect lenses attained so much, what may not the astronomer look for when science gives him lenses made from pure glass? If the heavens, by imperfect instruments, have so far been unveiled, to what extent may he not then be able to penetrate the pure ether, and reveal planets and heavenly bodies as yet unknown?

We close our reminiscences of Glass and its manufacture, by presenting to our readers a view of an American model glass factory of the present day.[4] By comparing this view with the sketches heretofore given of the early Venetian and French factories, they will perceive the very great improvement which is apparent over the ancient plans, an improvement conducing alike to the health and comfort of the workmen. Thirty years have passed in its development, during which many difficulties arose from the conflicting opinions of the English and German glass-makers; and, in fact, it was not until the proprietors boldly separated themselves from the current and influence of old, and almost fixed opinions, that any decided progress was shown in the development of manufacturing efficiency, or any plan contributing to the health and comfort of the workmen employed.

[4] See drawing No. 4, at end of book.

It is to be borne in mind that the first glass works in this country were established by the Germans, who used no other fuel than wood, the furnaces for window-glass constructed under their directions being for that fuel only; on the other hand, the English workmen who introduced the making of flint-glass had made use of no other fuel than coal, and the English were therefore obliged to adopt (for the want of coal) the German plan for furnaces, and adapt the same to the making of flint-glass. The house was like the furnace, half English and half German, and from the year 1812, for thirty years, little or no improvement was made in this particular. Year after year the old plan was followed, until necessity paved the way for new plans in the effort to secure a less expensive mode of melting glass.

The result has been highly favorable. More than one half has been saved in the melt, annealing leers, and working places, yielding the workmen greater space and facilities in performing their work, and no longer exposing them to the discomfort of extra heat, smoke, and unhealthy gases. These improvements have enabled the American manufacturer to sustain his business in the severe and trying competition with foreign manufacturers, who forced their glass into this country through their agents a few years since, in such quantities, and at such reduced prices, as seriously to affect the prosperity of our artisans; yet, aided as they have been by a tariff directly promoting foreign interest, and by the very low rates of wages paid on the Continent, they have been successfully contended with, and now a home competition has sprung up, reducing prices below a fair standard,--a competition, the result of enterprise, which will, erelong, regulate itself, for we fully hold to the maxim, that competition, honest and well sustained, is the soul and life of business:--

"No horse so swift that he needs not another
To keep up his speed."

There is no mechanical employment in this country yielding so good returns to the industrious as a good worker in glass, of the present day, can secure in the exercise of his skill. And we may still further say that there is no mechanical branch of industry offering such advantages for the full manifestation of a workman's real skill and industry, if the conventional usages which restrict the work could but be abrogated,--usages tending to a limited amount of work, and consequently making the workman to realize but a limited amount per week. Such workmen, of all others, should be allowed the inherent and inalienable right to work as long, and at such times, as the individual may deem for his comfort and interest.

We have expressed the opinion that the manufacture of glass is as yet but in its infancy. The experience of every day confirms the assertion, and illustrates the maxim that "life is short, art is long."

The time is not far distant when this country will become, we think, the largest exporter of glass, and the manufacture compose a most important item in every assorted export cargo. In this connection a hint to ship-owners may not be amiss. It is well known that in England, when a ship is put up for a foreign port, it is the custom to rate the freight according to the value of the merchandise,--dry goods paying the highest freight, hardware the next highest, earthen and glass ware the lowest. If our merchants would adopt this plan, very many of our bulky manufactures would find a market abroad; when, however, the same rate is required for a cask of glass ware as for a case of silks or prints, it taxes the latter a small percentage, but practically vetoes the export of the glass.

Our task is now ended; our object has been to give a simple and succinct outline of the characteristics and progress of the Glass Manufacture, to suggest such hints as might bear upon the further advance of the art, and the preservation of those practically identified with the manufacture, and, if possible, to attract the attention of those hitherto unacquainted with its nature and history. If we have neglected the maxim that "_those who live in glass houses_," &c., it has not been from the want of honest endeavors to remember it; and if we have contributed either to the instruction or the pleasure of any reader, (and this is our hope,) we shall not regret the hours spent in the preparation of this little work.

APPENDIX.

RECEIPTS, ETC.

There are plenty of receipts for the composition of flint or crystal glass, but no mixture that we know can secure a uniform shade in each pot. The component parts of glass are well known, and the mixer's sure guide is to watch the effect of heat on each pot, for he soon finds the mixture that gives good color in one pot will in another in the same furnace prove bad. If he possesses sufficient knowledge of the chemical causes, he can correct the evil.

Among the valuable receipts for rich colors is the following, for RUBY GLASS, which takes lead both in cost and richness:--

Take one ounce of pure gold; dissolve in a glass vessel two ounces pure sal ammoniac acid, and five ounces of pure nitric acid, which will take six to seven days; drop in at a time say one twentieth part of the gold. When the first piece is dissolved, drop in another twentieth portion of the gold, and so on until the ounce of gold is all dissolved. This will require twenty-four hours. Evaporate the solution to dryness. Then prepare in a glass vessel six ounces pure nitric acid, two ounces muriatic acid, and one ounce of highest proof alcohol; mix them well together, and drop in pure grained tin a bit at a time, _but beware of the fumes_. Stir it well with a glass rod; dilute the solution with eighty times its bulk of distilled water; then take the prepared gold, dissolved in a quart of distilled water, and pour it steadily into the solution of tin as above prepared, stirring all the while. Let it settle twenty-four to thirty hours; pour off the water, leave the settlings, pour in two thirds of a quart of water. Stir it thoroughly; let it settle thirty hours; pour off as before, and filter the precipitate through filtering paper. The result is the purple of Crassus. The ounce of gold thus prepared must be well incorporated with the following batch: say thirty-two pounds fine silex, thirty-six pounds oxide of lead, sixteen pounds refined nitre; melt the same in a clean pot, one little used, and smooth inside; when filled in, put the stopper to the pot loose, leaving it slightly open; leave it five or six hours, or time to settle, then a back stopper can be put up. In the usual time it will be ready to be worked out in solid, egg-shaped balls, and exposed to the air to be partially cooled; they are then to be placed in the leer under a strong fire, which will in two or three hours turn them to a red color; then the pans may be drawn slowly to anneal the balls.

It is well known to mixers that colored glass is derived from metallic oxides. To obtain the proper color depends on the purity and strength of the metallic oxides. The following receipts have with success been used:--

ALABASTER.

To 500 lbs. of batch add
30 " phosphate of soda,
10 " allumine,--_i.e._ calcined alum,
3 " calcined magnesia.

BLACK.

To 1400 lbs. of batch add
180 " manganese,
100 " calcined iron scales, made fine,
20 " powdered charcoal,
10 " arsenic.

CANARY.

To 100 lbs. of batch add
8 ounces best oxide of uranium,
1 dr. oxide of copper.

The common colors of purple, blue, emerald, or green, are too well known to require to be repeated here.

The following receipt for crystal glass is on the European standard, viz.:--

1200 lbs. silex,
800 " red lead,
440 " pearlash,
50 " nitre,
10 " phosphate of lime,
10 oz. white oxide of antimony,
24 " manganese,
32 " arsenic,
20 " borax.

GERMAN SHEET GLASS.

400 lbs. silex,
130 " soda,
126 " hydrate of lime,
4 " charcoal,
7 " nitrate of soda,
4 " arsenic,
1 " manganese.

Gold-colored spangles may be diffused through the glass by mixing gold-colored talcs in the batch.

AGATE.

To 150 lbs. flint batch add
10 " phosphate of lime,
6 " arsenic.

BLACK.

600 lbs. flint batch,
40 " manganese,
46 " oxide of iron.

LIGHT EMERALD GREEN.

200 lbs. flint batch,
2-1/2 " iron filings, calcined,
1/2 " antimony.

ORIENTAL GREEN.

110 lbs. flint batch,
1 " oxide of uranium,
2 oz. carbonate of copper.

OPAL.

500 lbs. batch,
60 " phosphate of lime,
4 " arsenic,
20 " nitrate of soda.

Said to turn without cooling.

William Gillender, of England, gives the following receipt for Bohemian Red, or Ruby:--

Sand, 62 lbs.
Lead, 76 "
Nitre, 22 "
Antimony, 8 oz.
Manganese, 3 "

Add one ounce of purple of Crassus to every eighty pounds of the above batch.

WAX RED.

To 15 lbs. flint batch add
1 " raw brass,
3/4 " crocus martus.

This he says is very good.

TURQUOISE.

To 1100 lbs. flint batch add
90 " phosphate of lime,
15 " arsenic,
15 " calcined brass dust.

VIOLET.

To 100 lbs. flint batch add
1 " calcined brass,
1-1/2 " zaffre.

Receipts for window-glass are as numerous as for flint. The following are in general use in England, so says Gillender:--

CROWN GLASS.

Sand, 1400 lbs.
Quick lime, 480 "
Sulphate of soda, 560 "
Charcoal, 25 "

PLATE GLASS.

Sand, 300 lbs.
Sulphate of soda, 450 "
Quick lime, 100 "
Nitre, 25 "
Charcoal, 5 "

DIAMOND GLASS.

Four pounds of borax, one pound of fine sand; reduce both to a subtile powder, and melt them together in a closed crucible set in an air furnace, under a strong fire, till fusion is perfect. Let it cool in the crucible, and a pure, hard glass, capable of cutting common glass like a diamond, which it rivals in brilliancy, is produced.

LEAD.

Lead is an important and costly ingredient of flint-glass, used as a protoxide, either as litharge or red lead, and should be perfectly pure, for the presence of any other substance or metal will be shown in the color of the glass. Consequently, the purity of the glass depends mainly on the quality of the metallic lead and its being well manufactured.

The writer believes he was the first person in the United States, aided by a director of the New England Glass Company, to build a lead furnace. This was in 1818. His only guide was a volume of "Cooper's Emporium of Arts and Sciences," which furnished a plan on a very limited scale.

The furnace proved successful, and enabled the Company to continue their manufacture of glass at a period when no foreign red lead was to be procured. They enlarged their works, until they have become the most important in the country; while for over thirty years they monopolized the business in all its branches, from the highest qualities of pure Galena and painter's red lead to common pig lead. In manufacturing metallic lead, its weight is materially increased by the absorption of oxygen gas. In 1847 the writer made many test experiments, one as follows: 660 pigs of blue lead, weighing 45,540 pounds, turned out from the ovens 48,750 pounds of litharge,--an increase in weight of 3210 pounds.

The cost of labor was $65.50; fuel, $86.50; engine power, $17.50; total, $169.50; and the market value of the excess in weight of the lead was $250, showing a satisfactory profit to the company for their outlay in this branch of their business. Chemistry gives the increase in course of manufacture: In protoxide state, 7 per cent.; in deutoxide state, 11 per cent.; in tritoxide, 15 per cent.

Muriatic acid will detect iron in lead, on dissolving a small piece of lead in the acid. If colorless, it is good.

Nitric acid will detect if there is cobalt in the lead, by adding to the acid half the quantity of high-proof alcohol. If present, the evidence is soon seen.

Some use the following as more direct:--In a small evaporating glass dish place say one ounce of lead; cover it with muriatic acid; dissolve the lead over a spirit lamp, add a little water, and let it settle; draw it off into another glass vessel, and add five or six drops of the solution of potash. If the lead is suitable for glass-makers, the solution will be of a light, clear, greenish color; if of a blue or purple shade, it is not suitable for flint-glass.

SAND, OR SILEX.

In the manufacture of glass it is essential that the silex should be perfectly pure, as the slightest mineral taint affects the color.

At first the New England factories got their sand from Demerara, brought as ballast, and the quality was good. During the War of 1812 this source of supply was cut off, but Plymouth beach provided for the wants of the manufacturers, until a better sand was discovered at Morris River, N.J., though not up to the full requirement of the art. For ten years past, Berkshire County. Mass., has furnished sand; the best quality is owned by G. W. Gordon, Esq. By thorough washing, and passing it through fine sieves, and proper packing, he now commands the market, and delivers it ready for use. The purity has been tested, as shown by the following extract from a report by Professor A. A. Hayes, M.D., of Boston, Massachusetts State Assayer, of the result of analyses of three samples of Berkshire sand, taken from three different locations owned by Mr. Gordon, viz.:--

"For the manufacture of glass, the slight amount of earth, in mica and tourmaline, contained in these samples, is of no account, the impurity being such oxides as color glass. The analyses therefore give only the proportion of coloring oxides; and, for simplicity of statement, the total weight of coloring oxide in each sample is determined in one part or pound.

"Sample B analyses: 4000 parts of this sample contain one part
of oxide of iron.

Sample C analyses: 3333 parts of this sample contain one part
of oxide of iron.

Sample P analyses: 3460 parts of this sample contain one part
of oxide of iron.

"Sample B is equal in purity to the best sand known as a material for glass, in this or any other country."

FURNACES.

Next to pots, furnaces are most important for the success of a glass manufactory. Long ago it was seen that the old English plan was defective. They consumed coal at an extravagant rate, though this was not a serious drawback in England, because the furnaces were located near coal-mines, and run with a quality called slack, not otherwise merchantable. English furnaces were constructed with reference to durability, usually eight feet in diameter at the interior base, and six feet clear at the crown. This rule was followed in this country until 1840. The writer, having occasion to build an extra furnace, adopted the novel plan of one fourteen feet diameter at the base in the clear and only five feet at the crown, braced by binders, with cross-ties to prevent lateral expansion, which was a success.

A furnace on the old plan consumed 2575 bushels of coal weekly, and refined only 38,000 pounds of raw material. The new refined 35,000 pounds, with a consumption of only 2000 bushels of coal. Since then a further decrease in consumption of coal has been produced by the use of the Delano patent, which feeds the furnace by forcing up the coal at the bottom of the burning mass, thus consuming the entire smoke, and obviating the necessity of wheeling coal on the glass-house floor and impeding the workmen. It also does away with all danger to the pots in feeding the fires. Besides these great advantages, it distributes a regular and uniform heat to each pot, causing the pots to last much longer, and fusing the metal better,--important items to mixers.

From three to five tons of fuel is the weekly saving in a first-class furnace.

It is of vital importance to obtain pots that will last a reasonable time. Clays of the finest quality are essential. Each piece must be freed from any foreign matter, particularly sulphate of iron, which often occurs. The burnt and raw clay should be well mixed, wet, and frequently kneaded, or trod over by the naked feet. Tenacity must be secured, sufficient that a roll twelve to eighteen inches long can be suspended, and hold firmly together by its own adhesiveness. The next point is to make the pots free from air blisters, all portions being compact; then to dry them thoroughly, which requires great care on account of the inequality of the different parts. Pot-makers are not agreed as to the value of different clays, and the use and proportion of raw to burnt shells. Some use sixteen parts raw to eleven burnt, some fifty-five raw to forty-five burnt, some equal proportions of each.

Manufacturers have mainly depended upon imported clays, but the Western glass-makers have used Missouri clay with success. In the east it has not yet come into general use. Of the imported, that from Stowbridge is considered best. Garnkerk is a strong clay, and, if well selected, will rival any other. The analyses are for

STOWBRIDGE,

Silica, 64 parts,
Alumina, 20 "
Lime, 1 "
Iron, 3 "

GERMAN,

Silica, 46 parts,
Alumina, 34 "
Iron, 3 "

GARNKERK,

Silica, 53 parts,
Alumina, 43 "
Lime, 1 "
Iron, 1 "

FRENCH,

Silica, 40 parts,
Alumina, 31 "
Iron, 3 "

WESTERN,

Silica, 49 to 52 parts,
Alumina, 31 to 32 "
Iron, 2 to 4 "

FUEL.

This subject deserves special notice. We have said that the New England manufacturers at first used wood only, which was prepared by being split into equal lengths, with an average diameter of two inches, and then kiln-dried to dispel the sap and moisture. This fuel was supplied to the furnace at opposite fire-holes, a stick at a time, which was a laborious and heating process.

Subsequently, a furnace was built at South Boston, over a cave, and unkilned wood was used in clefts. This saved one quarter in fuel, but it used up the pots so rapidly as to prove to be no economy in the end. After the development of the Virginia coal mines, our furnaces were altered to use coal, which proved to be more convenient and less costly than wood. The Pictou and Cumberland mines also increased the supply; and at present all the furnaces in New England, with one exception, are run with this last-named fuel.

The various experiments made to economize fuel for the "glory-holes," as the workmen call the working places above the furnace, are well known. For many years the prepared wood we have spoken of was used. Then resin in a powdered state was added, which was both inconvenient and dangerous,--it having caused the destruction by burning of two glass-houses. This risk was finally overcome by the introduction of an invention which used it in a liquid state. But the demand for resin became so great as soon to more than double its price. This led to the substitution of coal tar, which was in use until science discovered its latent virtues for other purposes, and largely increased the original cost of the material. Indeed, at first the gas companies had considered it of no value, and had thrown it away by thousands of barrels. Combined with dead oil it is still used by glass-makers, but at greatly enhanced prices.

The Cape Cod Glass Company have had in use for several years a Delano patent furnace-feeder, which enables them to use both hard and soft coal, as either is cheapest, and consumes the smoke and gas of either fuel, thus doing away all annoyance to the neighborhood. Theretofore every attempt to run working places with hard or soft coal had failed on account of the noxious gases set free, which injure the color of the glass. But owing to the intense heat created by the Delano patent, the furnace consumes these gases, and gives a quick fire polish to the various articles finished therein.

As our native supplies of hard and soft coal are inexhaustible, there is no likelihood of an increase in the price of the present fuel so as to necessitate, as heretofore, a substitution of some cheaper article, especially as the discovery of petroleum tends to cheapen coal by a diversion of a portion of its consumption to that useful mineral oil.

USEFUL ITEMS.

A bushel of English coal weighs 80 pounds: of Virginia coal, 93 pounds; of Pictou, 76 pounds; of Cumberland, 84 pounds; of red ash, hard, 84 pounds.

Crude saltpetre, refined, loses nine per cent.

Chemists estimate that one hundred pounds of pearlash contain thirty per cent. carbonic acid. In refining, it loses on the average fifteen per cent. in weight.

Phosphate of soda brightens glass.

Borax brightens, but hardens glass.

Twenty-five silver dollars refined will give thirty-seven ounces of nitrate of silver.

A square foot of furnace clay weighs one hundred and twenty pounds.

Alum, calcined, loses in weight sixty per cent.

Crude flint batch, melted and ladled out, loses in the average fifteen per cent. in weight.

Hard coal will measure forty cubic feet to a gross ton.

Glass in water. There are some peculiar phenomena connected with hot glass and water. If a ball of red-hot iron is placed in a vessel containing cold water, the latter is quickly agitated. But a ball of melted glass of equal weight dropped in cold water will produce no immediate agitation. The water will remain for some time quiescent; but when the glass is cooled to about half its highest temperature, it agitates the cold water violently.

Technical terms, descriptive of glass, such as crystal, flint, tale, may be derived from these facts: the French used for their base crystal stones, burnt and ground fine; in England they had recourse only to flint stone, treated the same as the French used their blocks of crystal; tale was derived from the mode of selling, the best glass being sold only by weight, while light articles were sold tale.

End of Project Gutenberg's Reminiscences of Glass-making, by Deming Jarves