Chapter III: Blues (3)

“Endemann considers that the blue colour is due to a ‘colour nucleus,’ consisting of unchanging proportions of aluminium, sodium, oxygen and sulphur, in each variety of ultramarine the proportion being different, while the rest of the sodium and aluminium and the whole of the silica merely act as a vehicle necessary to the preparation and existence of the colour. He considers that this ‘colour nucleus,’ in the case of white ultramarine, which he calls the ‘mother-substance in the manufacture of blue ultramarine,’ has the formula AlNa_{4}O_{2}S_{2}. By the action on two molecules of this of sulphurous acid gas, Na_{2}O is removed, and green ultramarine Al_{2}Na_{6}O_{3}S_{4} is formed, which then, by the action of oxygen, which forms sodium sulphate, passes into the pure green compound, having the formula Al_{2}Na_{4}O_{3}S_{3}. In the ‘indirect process’ of manufacture, green ultramarine is converted into blue by being burned with sulphur. By this means Endemann considers that more sodium and sulphur are removed, and blue ultramarine Al_{2}Na_{2}O_{3}S_{3} is formed. He considers that the other portion, not included in the ‘colour nucleus,’ differs in different samples. In one which he mentions it has about the composition 3Al_{2}O_{3}.5Na_{2}O.16SiO_{2}.

“But of all chemists who have worked on this subject, none has done more to increase our knowledge of ‘the blue marvel of inorganic chemistry,’ as he himself has called it, than Reinhold Hoffmann. His position of manager of the Marienberg Ultramarine Works, near Benscheim, in the Grand Duchy of Hesse, renders his acquaintance with the manufacture perfect, and his untiring researches on the subject have been well rewarded by results both interesting and valuable. He considers ultramarine to be a double silicate of sodium and aluminium, together with bisulphide of sodium, the variety poor in silica, characterised by its paleness and purity of tint, and easy decomposition by acids, having the formula 4(Al_{2}Na_{2}Si_{2}O_{8}) + Na_{2}S_{4}; while that rich in silica, characterised by its dark and somewhat reddish tint, and more difficult decomposition by acids, has the formula 2(Al_{2}Na_{2}Si_{3}O_{10}) + Na_{2}S_{4}. He also considers it very doubtful whether green ultramarine is really a chemical compound, and indeed it is now generally considered that the colour is only due to small traces of sodium salts in very intimate mechanical mixture with the blue variety, for by heating the green body for some time at 160° with water in closed tubes, it is converted into the blue product, and small traces of sodium compounds are found in solution in the water; and further, on heating blue ultramarine strongly with sodium sulphate and charcoal--that is, acting upon it with sodium sulphide--the green variety is formed.

“In a paper by Knapp, an abstract of which appeared in the _Journal of the Chemical Society_ for March 1880, there are some curious facts recorded with regard to the colouring agent. It was noticed that when silicic acid was replaced by boracic acid, a blue, nearly as stable in its properties as that of ordinary ultramarine, was produced. It was found that a blue could be obtained without alumina being introduced. Hence silica without alumina, and alumina without silica, can be employed with a certain amount of success. The blue, however, formed without silica, is not so strong or stable as that formed with it.

“One very curious property which ultramarine possesses is its power of giving up its sodium in exchange for other metals. Thus, by heating blue ultramarine with a concentrated solution of silver nitrate in sealed tubes to 120° for fifteen hours, a dark yellow _silver_ ultramarine is produced, containing about 46·5 per cent. of silver. This corresponds to about 15·5 per cent. of sodium, which is just about the amount that the original body contained.

“When this body is heated with an aqueous solution of sodium chloride to 120° in sealed tubes, about three-quarters of the silver is replaced by sodium, but the other quarter cannot be so replaced; in fact, blue ultramarine, when heated with silver chloride, takes up silver, and becomes green. But by heating silver ultramarine with sodium chloride in the dry way, at rather a higher temperature, the whole of the silver is replaced by sodium, but the ultramarine thus regenerated does not equal the original body in colour. The change is probably due to the loss of sulphur in the formation of the silver ultramarine.

“If in the above experiment potassium chloride be substituted for the sodium salt, and the temperature not allowed to exceed 400°, a bluish-green _potassium_ ultramarine is formed. _Barium_ ultramarine is a yellowish-brown product, _zinc_ ultramarine is violet, and _magnesium_ ultramarine is grey. These may all be obtained by acting on the yellow silver ultramarine with the corresponding metallic chloride.

“From the experiments of Dollfus and Goppelsröder some very striking differences have been brought to light between the three types of colour which they examined--namely, the blue, green and violet--in their behaviour with various reagents. Thus, an aqueous solution of caustic soda or potash does not act on the blue or green, but turns the violet to blue, and when heated with carbonic oxide the same result ensues. Many other reagents have the same effect on the violet variety, but when acted upon with sodium sulphide, the green turns grey, and when heated with potassium chlorate becomes darker and loses its brightness of colour. Dollfus and Goppelsröder attempt no explanation of these facts, but simply state them as results of their observations, and profess their inability to give any chemical formulæ for the three ultramarines, though they consider that there is sufficient proof that each has its distinct constitution. They give as their opinion, however, that they are double silicates of aluminium and sodium, in which a part of the oxygen is replaced by sulphur.

“Violet and red ultramarines are more bodies of scientific interest than of any practical use, as their colouring power is not sufficiently great. The violet variety may be prepared by exposing the underground blue product to chlorine gas under a high temperature, while the red may be obtained from the violet by acting on it, under a low temperature, by dilute nitric acid fumes.

“The first artificial method of producing ultramarine was that known as the ‘indirect process’--that is, first the manufacture of green ultramarine; and secondly, its conversion into blue. It was carried out as follows:--

“An intimate mixture of Glauber’s salts, china clay, and coal or rosin, finely ground together, was placed in crucibles and baked or burned in an oven for about six hours. It was then transferred to iron trays, and heated with flowers of sulphur to the point where the sulphur took fire, when it was allowed to burn itself out. By this second process the green was converted into blue. It was then washed, ground with water, and settled out, the first deposit being of a darker shade than the second, and the colour becoming lighter as the powder settled was finer in grind. This is essentially the method employed now at many German works--those at Marienberg, for instance--and produces what is known as “sulphate ultramarine,” distinguished by its pale shade and almost _greenish_ blue tint.

“There are, however, some objections to the indirect process, and it was considered advisable to find a plan by which ultramarine could be made in bulk in a muffle furnace. The following is a method which is employed at the present time in some of the German works:--

“A mixture of china clay, carbonate of soda, sulphate of soda, sulphur, sand and charcoal or rosin, finely ground together, are placed upon the floor of a muffle furnace, being pressed down so as to present an even surface. The mixture is then entirely enclosed with fire-clay tiles, the spaces between which are filled in with thin mortar. When the oven is so charged, the front is built up, a small hole being left for watching the temperature of the flue between the tiles and the top of the furnace, and for drawing samples during the process, which is done through a corresponding hole in the front of the fire-clay tiles, temporarily closed with a fire-clay stopper. The oven is now heated, slowly at first, and afterwards more strongly, so that at the end of eight or nine hours it is at a dull red heat. It is kept at this temperature for about 24 hours, when the heat is raised so that a clear red glow is obtained, which is kept up to the end of the operation.

“For the purpose of taking a sample, an iron spoon borer is introduced through the hole left in the enclosing tiles, turned round, and pulled out. The contents are laid on a clean tile, and quickly covered with another tile, on which a second quantity is placed, and allowed to remain exposed to the air. If the oven has been sufficiently heated the covered sample should appear of a bluish green, and no longer brown or yellow, while the second sample should be rather bluer. If this be the case, the oven is heated slowly for another hour, and then all communication with the outer air is cut off. It is allowed to cool and then opened, when the contents should appear as a beautiful blue mass, the lower portion of which, however, is of a greenish tinge. Both parts are now treated alike, but worked up separately, the greenish-blue portion making an inferior article. The finishing process is as follows:--

“The raw ultramarine is ground in upright mills, and then repeatedly boiled for about ten or fifteen minutes at a time in cast-iron boilers, being all the time agitated by a mechanical stirring arrangement. It is then allowed to settle, and the water is drawn off with a siphon. As soon as the powder settles into a hard compact mass, it has been sufficiently washed, and it is then dug out. The part next to the bottom of the boiler is generally coarse and of poor quality. It is carefully separated from the upper portion, which is transferred to wet mills of the ordinary description, and there ground for six to twelve hours, during which time about 150 lb. can be treated in each mill. The ground colour from these mills is then collected in a large tub, and allowed to settle for four hours, during which time the coarsest particles fall to the bottom. The liquid is then passed through a series of tubs, in each of which it is allowed to stand for a period of time, lengthening as the quality settled out becomes finer, the last settling requiring about three weeks. The various qualities are then dried and sifted, when they are ready for the market.

“The blue produced by this operation is of a good quality, but there are some objections to the process, which have given rise to another, in which the ultramarine is produced direct in crucibles similar to those used in the indirect process.

“This is conducted as follows:--The mixture of raw materials consists of about 100 parts of china clay, 90 of carbonate of soda, 110 of sulphur, 20 of charcoal, and a quantity of infusorial earth, varying according as the ultramarine produced is desired to be rich or poor in silica. These are finely ground together, in which process great care must be observed, as much depends upon its being properly carried out. The mixture is then filled loosely into crucibles provided with flat circular lids, which are fixed on with mortar containing clay. This is allowed to dry, and the crucibles are then ready for firing, which process is conducted in ovens, generally constructed so as to contain several hundred crucibles, which are arranged in rows one above another.

“The mixture undergoes a very curious change of colour while in the ovens. When put in it is greyish white, and during the process of burning it becomes successively brown, green, blue, violet, red and white, in the order named. These changes are, according to Guimet, due to oxidation. The brown appears with the blue flames due to the combustion of the sulphur, the green just after the sulphur flames have ceased, and the blue is first formed at a temperature of about 700°--i. e. a bright red heat. If, after this, heat be still applied and air freely admitted, the mixture becomes first violet, then red or rose coloured, and finally white. When this white body is heated to redness with carbon or other reducing agents, the red, violet, blue, green and brown colours (according to the amount of reducing agent employed) may sometimes be reproduced, though the reaction is by no means a certain one.

“If brown ultramarine be removed from the oven, and allowed to remain exposed to the air, it immediately takes fire and burns to an inferior blue colour. The same thing occurs with the green body. Even if the brown product be completely cooled before being exposed to the air, it will, as soon as the air is allowed to reach it, get hotter and hotter, until it is glowing, when it will burst into flame and become blue. Attempts have been made to preserve the brown colour, which is of a beautiful chocolate tint, but have always failed. In one instance, when this was tried, the colour was put immediately into water, and treated like the ordinary blue variety, and as long as it was kept moist no change was apparent. After being washed and wet ground the moist powder was put into a cask, where for some time it was allowed to remain undisturbed. At the end of about three weeks it was noticed that the mass was hot, and on being turned out of the cask and broken up it was found to be at a glowing heat in the interior.

“After the oven has been fired for several hours, it is carefully closed at every point where air might enter, and allowed to cool for four or five days. The exact length of time during which the ovens are fired, and the amount of air admitted, depend upon various circumstances, one important one being the state of the weather. Thus, on a dull, foggy day, when the draught in the chimney is not good, a longer time is required. Of course, no rule can be given for this, and it is the experience required in the management of the oven that makes the manufacture so difficult to carry out successfully, the early efforts of a manufacturer not unfrequently resulting in the loss of a whole ovenful of raw material. As soon as the oven has cooled, the crucibles are taken out, and the contents of each are turned out in a solid mass, which must be carefully cleaned with a knife of any badly burned portions, and afterwards broken up and thrown into a cask along with the contents of other crucibles.

“This forms what is known as crude raw ultramarine. It contains about 15 per cent. of sulphate of soda, which must be removed before the colour is fit for sale.

“For this purpose it is washed with hot water in large tubs, after which it is ground in wet mills to an impalpable powder, and allowed to stand for about an hour in a large tub, in order to remove the coarsest particles and dirt which are sure to be present. It is then removed to another tub, where it settles for four or five hours, and from this it passes to others, where it stands for various lengths of time, increasing, of course, as the powder to be settled becomes finer, the last settling occupying three or four weeks, and producing the strongest quality that can be obtained--that is to say, it will bear mixing with more of a reducing medium, such as mineral white, than would a former settling for the mixture in each case to be of the same depth of colour.

“The water, after the final settling, still contains about 5 per cent. of ultramarine. This would take five or six months to settle, and as this time could not generally be given to it, it is precipitated with lime water, which has a sort of coagulating influence upon the particles, which can then be removed by filtration. It is a curious thing that this last quality is quite different from the one preceding it, being very inferior in both colour and strength.

“After settling, all the various qualities are dried in kilns, and sifted through fine brass wire sieves by means of a fan, which breaks up the lumps and forces the particles through the meshes of the sieve, which must be very close--about 100 to the inch--in order that the ultramarine may be perfectly smooth and free from lumps or grit of any sort. When finished, it should be in the form of an impalpable powder--the finer qualities so fine, indeed, as to feel almost _buttery_ when rubbed between the fingers. After this process the different qualities and shades are mixed to certain standards, and are then ready for sale.

“The uses of ultramarine in the arts and manufactures are very numerous and important. The most important, from the point of view of quantity, is the manufacture of ‘square blue’ for washing purposes. In the preparation of this article the ultramarine is generally mixed with bicarbonate of soda and some glutinous material, to help it to retain its shape, and is then pressed into the well-known form of small square or oblong blocks.

“It is also used largely in the manufacture of blue paint and printing ink, and in the preparation of blue mottled soap. The way in which it is employed in the last-named manufacture is worthy of remark. It is added to the soap while it is in a molten state and just before it is allowed to cool, and thoroughly mixed with it, so that the whole mass is of a pale blue tint. If a small quantity of this be removed from the boiler and cooled quickly, it remains of a uniform tint, but in the case of the whole boilerful, where the cooling is very slow, the action is entirely different. Just at the point of cooling, when the soap is going to set hard, the ultramarine--to use a technical expression--“strikes,” and goes into the form which gives to blue mottled soap its well-known appearance.

“In the manufacture of paper, ultramarine also plays an important part. It is here used not only for producing blue shades, but also as a bleaching agent, to counteract the yellow when white paper is made.

“Another important use is in the calico manufacture, where it is used both in the printing of blue patterns and in the finishing of goods. In the case of calico printing, it is mixed with albumen and printed on to the calico, which is then subjected to the action of steam, the albumen being by this means coagulated and each grain of ultramarine surrounded by an insoluble envelope, so that it cannot be washed out of the calico.

“The growth in the manufacture of ultramarine has been very remarkable, especially when it is considered how little the process is understood chemically, and what care and patience--to say nothing of the equally important item of capital--are required in the starting of a manufactory. Commencing less than 50 years ago in the works of Guimet, at Lyons, who produced 120,000 lb. annually, there are at the present day nearly 40 manufactories at work in various parts of the world--chiefly in Germany--producing about 20 million lb. per year. The following figures will give some idea of ten years’ growth of this industry--from 1862 to 1872:--

1862. 1872.

Number of manufactories 24 32
Men employed 964 1929
Tons manufactured 3556 8585

“From the above numbers it will be seen that in these ten years the manufacture more than doubled itself, the fact being due, however, not so much to the increase in the number of works, which was only one-third, as to the enlarged capabilities of those existing in 1862. Thus, in the works of Dr. Leverkus, near Cologne--the first works ever started in Germany--the number of men employed had, during these ten years, more than doubled, while the output had trebled; and in the case of the Marienberg Works the difference was even more striking, the number of hands employed and the quantity turned out per annum having nearly quadrupled.”

In reply to various questions which were asked in the discussion which ensued, Mr. Rawlins said that, with regard to the use of ammonia soda, it had frequently been used in the manufacture of ultramarine, and was constantly used he understood, but he himself had not much experience of it. As far as he could make out, it certainly produced ultramarine, but of a darker shade than that made with Leblanc soda. It could not be supposed, in works where the Leblanc soda was used, that ammonia soda could conveniently be substituted, for of course a works when established had to adhere to its known standards and shades, and it would not do to change the raw materials, though the ammonia soda produced a very good ultramarine. As regards the discovery of ultramarine, the first works started anywhere were Guimet’s. He had with him a little historical list containing the dates at which the various works established before 1866 or a little later had been started. It was drawn out by Hoffmann, who, as he stated before, was the manager of large ultramarine works, and he put down Guimet’s, which were started in 1829, first on the list. Dr. Leverkus started in 1834. He knew that the discovery of ultramarine had been attributed to different people. He had mentioned Guimet because it had generally been considered, as far as he had heard, that Guimet and Gmelin were the two who discovered it from a manufacturing point of view. He had heard of crystals of ultramarine, but had never seen any, and he knew they were very difficult to prepare, and very rare. He had mentioned that the grinding had to be done very thoroughly, because the better it was mixed and the finer it was ground, the better was the ultramarine produced. If it was badly mixed it was quite fatal to getting a good result. Grinding lightens the colour. Raw ultramarine must be ground before it was practicable to use it at all. For instance, a coarse ultramarine could not be used for printing calico. Therefore it was necessary to grind it both for the sake of the colour and for the sake of the way in which it was applied. It was increased in value by grinding because it made it stronger and finer. Before grinding it was of a dark colour, but after grinding it became lighter and brighter.

The materials employed in McIvor’s process for making ultramarine are kaolin or other suitable clay, a solution of sulphide of sodium, in which sulphur in the form of flowers of sulphur is dissolved to saturation, and caustic or carbonate of soda.

The preparation of the solution is effected by adding the sulphur to boiling sulphide of sodium liquor of maximum strength until it ceases to be taken up. The clay and soda are first roasted together at a red heat, so as to effect a partial double decomposition, and the product, after grinding, is made into a thick paste with “sulphur liquor,” i. e. the sulphide of sodium solution of sulphur. This latter operation may be carried out in an ordinary pug-mill. The paste so formed is dried in an oven or other convenient way, and the dried mass (being broken into small pieces) is roasted without access of air in a closed earthenware retort, first at about 480°-570° F. for an hour, then at a red heat for eight hours, and finally at a moderate heat just below dull redness, in presence of a slow current of air, which enters through a series of holes or small openings in the front of the retort, the current being regulated by means of a damper or an adjustable slide. The retort should be allowed to become quite cold before being opened, otherwise the tint of the product will be injured.

McIvor has found the following proportions of the raw materials used in the process to yield excellent results, viz:--

Sulphide of sodium 42 lb.
Sulphur 20 “
Kaolin (china clay) 110 “
Soda (as carbonate) 106 “
or
Caustic soda 40 “

These quantities yield about 2 cwt. of ultramarine blue.

The following communication from the pen of J. B. Nejedly, of Vienna, appeared in the _Chemiker Zeitung_, during 1888:--

“Animated by various articles and notes in your journal under the heading of ‘The Present Position of the Manufacture of Ultramarine,’ I would like to draw out of obscurity a little work on this industry which contains much that is true, and furnishes at the same time many comparisons with regard to the present position of the ultramarine industry in Germany.

“The work above referred to was printed in the year 1840 and bears the title:--

“‘Treatise on the chemico-technical preparation of Ultramarine
colours, according to the discoveries of Leykauf and Heyne, or on
the importance of the manufacture of blue and green Ultramarine for
purposes of science, art, and industry. By Friedr. Wilh. Heyne,
president of the Nürnberg Ultramarine Manufactory. Nürnberg: 1840.
Printed at the Campe Press.’

“The preface, which I consider to be well suited to present circumstances, I reproduce verbatim, while from the little work itself I will only quote such sentences as would seem to be suited to the present time, and which are the most important as bearing on the subject.

“‘_Preface._--The incitement to this treatise was furnished by the utility of the discovery of Leykauf, instructor of chemistry at the technical schools in Nürnberg, of artificially preparing the well-known blue mineral colour styled ultramarine, according to simple principles, which discovery was supplemented by the production of the green ultramarine, an equally genuine and beautiful green mineral colour, by the technist Heyne in Nürnberg. A short review of the importance of these two discoveries for mankind in general and for science, art, and industry in particular, will form the main subject of this treatise, which has no other object but that of arousing the attention of all high protectors and stimulators, as well as friends of industry and art, to a newly-born industrial branch. At this moment we are living in a period when many industries have got into the stocks, in consequence of far too severe competition, combined with other influences; indeed they are barely able to support those engaged in them. If in consequence of this state of things it already becomes of the most vital importance that fresh sources of acquisition should be obtained, it becomes all the more so when by their means at the same time materials come into requisition which the Fatherland possesses in great superfluity, and which otherwise possess no intrinsic value beyond just the expense of extracting them from their natural localities or deposits, and the worth that attaches to their working up for industrial purpose. A source of acquisition in this sense is met with in the manufacture of blue and green ultramarine colours, which in course of time can be raised to an extremely valuable acquisition. May the communications here made result in their being considered worthy of a thorough many-sided investigation and consideration.’

“REGARDING THE WORK ITSELF.

“Page 21.--‘Not long since a prize of 6000 francs was offered by the “Société d’Encouragement.” This prize was gained by Guimet, who has not published his process, and who now furnishes ultramarine at the price of 25 francs per oz., whereas it otherwise cost 200 francs per oz. Latterly, in 1839, Guimet reduced his price for ultramarine, viz. No. 1, for painting, to 10 francs, a lighter shade being 6 francs per oz. In addition, this manufacturer furnishes lower qualities for carpet and paper manufacturers at 20 francs and 12 francs per lb.’

“Page 23.--‘Indeed, if we are able to produce ultramarine by means of a polysulphide of sodium and common clay, then the most beautiful and most lasting of all known blue colours would at the same time become the cheapest of them all.’

“Page 27.--‘All faults which are known to exist in the old methods are obviated in the new invention of Leykauf and Heyne, while the same offers the following advantages:--

“‘(1) The materials which are treated with it can be brought into use without any special previous chemical preparations, indeed as supplied by Nature, while chemical treatment is entirely unnecessary. In view of the unimportant cost of derivation of the raw material, there cannot consequently be any questions raised with regard to waste.

“‘(2) This method is so simple that any man of sound intellect can easily work it, without possessing any special chemical knowledge beforehand. As the labour can be easily grappled with, errors can only occur when the grossest carelessness is shown in conforming to the instructions prescribed.

“‘(3) According to the said method one can work according to any desired scale, and, what is best of all, the larger this scale the more favourable are the results obtained, lighter work and excellence of quality.

“‘(4) If the process is carefully conducted, everything is in your own power, nothing depending on chance.

“‘(5) Consequently an equal product can invariably be obtained, while this can at will be brought to the most complete stage of perfection at but little greater cost than lower qualities entail.

“‘(6) According to this method you are master of the fire, enabling a retention of colours in any desired shade, of the deepest tone, of the greatest permanency.

“‘From this it appears: That this process is the easiest, the cheapest, and the most complete. Worked according to this method the hope is likely soon to become a reality that ultramarine may yet become the cheapest of all mineral colours, and as in the same everything rests upon simplicity, the preparation of the article in future will be carried on somewhat after the fashion of baking, brewing, &c.’

“Page 32.--‘Moreover, there is not only blue ultramarine, but also a pure green, and we may venture the hope that similar combinations in white, black, red, and yellow will soon follow in equal perfection. In consequence of these discoveries, Leykauf and Heyne have erected a factory in Nürnberg, which, according to a circular dated 15th July, 1840, is in operation under the style of “Leykauf, Heyne and Co.,” and are producing the two ultramarine colours referred to at the present time at the rate of 50 lb. per day.’

“Page 33.--‘All the mechanical appliances of the factory are at the present time exclusively worked by hand, the number of persons employed being sixteen; while the establishment upon completion of the buildings that are wanting is calculated to employ twenty operatives and two horses. With this extension the factory will be able to turn out 5 cwt. blue and 5 cwt. green weekly, consequently annually 500 cwt. of finished merchantable ultramarine will be brought on the market.’

“Page 35.--‘Now, as regards the prices ruling at present for Nürnberg ultramarine, these are, as compared with those of the French, more than 500 per cent. cheaper. Blue ultramarine costs, namely, in Nürnberg, quality No. 0, 10 florins per lb.; a lighter quality, which is nevertheless darker than the darkest French at 100 francs, 5 fl. per lb.; a third quality likewise darker than the seconds French at 60 francs, 3 fl. per lb. Green ultramarine, 3 fl. 10 kr. per lb.

“‘How much further, however, these low prices will be yet reduced after the completion of the factory, may be gathered from a detailed calculation of cost which the chief of this factory has made himself responsible for as being the highest estimate. This calculation of cost is based upon the weekly production of 10 cwt., which the factory will soon be able to turn out, and upon a necessary cost of plant and working capital of 90,000 Rhenish florins, as follows:--

“Page 36.--‘Calculation of cost of 500 cwt. blue and green ultramarine:--

Fl.

(1) Raw material and cost of transport 10,000
(2) Fuel, including cost of transport of 7200 cwt. of
coal at fl. 1.30 10,800
(3) Wages of 20 operatives at fl. 250 per annum 5,000
(4) Utensils and apparatus 3,200
(5) Buildings and repairs 3,400
(6) Keep for two horses 600
(7) Expense of factory 3,000
(8) Cost of administration 2,000
(9) Unforeseen matters and accidents 2,000
(10) Interest on building and working capital at 5
per cent. 4,500
(11) Public taxes, insurance, &c. 500
------
Thus 500 cwt. will cost Fl. 45,000
“ 1 “ “ Fl. 90
“ 1 lb. “ 45kr.

“‘Forty-five kreutzers, therefore, in accordance with the above, will in future be the production cost of a colour which, as is well known, could not be obtained for several hundred guldens, while in green it was not procurable at any price.’

“I venture to hope that the foregoing communication may yet prove of some interest in chemical circles.”

1 florin or gulden = 2_s._ 1 kreutzer = ½_d._

Ultramarine is by far the most commonly used of the blue pigments. It is a chemical combination of silica, alumina, soda, and sulphur, but its exact chemical constitution is not known, the proportions of its ingredients varying somewhat with different makes. There are two principal varieties of ultramarine sold. One is known as sulphate ultramarine the other as soda ultramarine, from the materials used in the process of manufacture. In the first, silica, china clay, _sulphate of soda_, and coal are used; in the latter, silica, china clay, _carbonate of soda_, and sulphur are used. The sulphate ultramarine is distinguished by its very pale greenish blue colour, while the soda ultramarine is of a violet hue.

Ultramarine is distinguished from other blues by the fact that acids completely decolorise it, with the evolution of sulphuretted hydrogen and the formation of a white precipitate of sulphate.

The sulphate ultramarine is more easily decomposed by acids than the soda ultramarine, and some makes of the latter more easily than others. Alkalies and heat have no action on this pigment. Boiled in strong nitric acid, ultramarine is completely decolorised, a colourless solution being formed, and a gelatinous mass of silica being left as a residue.

It is not as a rule necessary to make an analysis of the pigment; the above tests serve to distinguish it from other pigments.

An assay of ultramarine should include the following points:--1st, colour or tint; 2nd, covering power or body; 3rd, acid resisting properties: this can be tested by making a very weak solution of sulphuric acid--about 4 oz. in 1000 oz. of water--and adding a little of this to the pigment contained in a glass, and noting how long it takes to bring about decolorisation; 4th, the power of resistance to the action of alum. When ultramarines are boiled with a solution of alum, they are more or less reddened thereby; those which are made with a large excess of silica are found to resist this action of alum better than those containing a normal quantity of this compound. Such ultramarines are preferred by the paper maker, who uses a large quantity of alum and sulphate of alumina in the sizing of his papers, and therefore he wants an ultramarine which shall not change in shade when used for tinting alumina sized papers. This point is easily tested. A solution of alum is made, and in a little of this a small quantity of ultramarine is boiled for a few minutes, and it is noted whether any change of shade occurs. If any sample is found to change much, that sample must be rejected for paper tinting, although it may be used by the painter or the laundress.

It may be worth pointing out here that ultramarine should not be used with any other colours which have a tendency to be acid, as sooner or later the colour will be destroyed. It should also not be used with lead or copper pigments, as the sulphur it contains tends to react on those metals; forming the black sulphides, thus leading to the ultimate discoloration of the mixture.--(_Chemical Trade Journal_).