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spread. This may be accomplished by adding a small quantity of whiting to the pigment while grinding it; the workman can then load his blocks with colour, and, consequently, give a thick coating to the impression or print made by it.

XXXV.-On a singular Galvanic Pile. By Mr. F. WATKINS, Philosophical Instrument Maker, London*. THIS pile is constructed with a single metal only, and without the use of any liquid. It consists of from sixty to eighty plates of zinc, each four inches square, fixed in a wooden trough or frame, at a short distance from each other, and having only a thin plate of air between them. One side of each plate is smoothed and polished, but the other side is left rough. The polished faces are all turned in one direction. If one extremity of the pile be made to communicate with the earth, and the other with an electroscope, the latter will immediately indicate the presence of one or the other of the two electricities, according to the pole with which it is brought in contact. The humidity of the air favours the action of this pile, which may be considered as a kind of dry pile, in which the air is substituted for the usual paper discs; and the two surfaces of the zinc plates perform the office of the two heterogeneous metals usually employed. It appears to be to the stronger oxidation of the polished surfaces of the zinc plates, that we are to ascribe the developement of electricity in each plate; the intermediate strata of air, and perhaps the frame, permitting this electricity to accumulate, as in the ordinary pile.

* From Annales de Chimie et de Physique.

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XXXVI.-On a new Use of the Chromate of Potash. By M. KAECHLIN-SCHOUCH*.

THE new use of this chromate is to print a white pattern on a blue or green ground. A blue dye is first given to the cloth, by means of the indigo vat, more or less deep, according to the green required; the cloth is then prepared with the aluminous mordant, and passed through hot water, it is then again prepared with an ungummed solution of bichromate of potash, consisting of two and a half ounces of salt, to four pints of water. It is then printed with the following preparation :

Water thickened by roasted starch
Tartaric Acid.

Oxalic Acid

Nitric Acid

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The nitric acid is unnecessary, except for delicate designs. The moment this substance is printed, the blue colour is destroyed; the cloth is then instantly put into running water, and afterwards dyed in quercitron, or other dye stuffs.

This destruction of vegetable colour arises from the following general fact: whenever chromate of potash is mingled with tartaric or oxalic acid, or with a neutral vegetable substance, and a mineral acid, as the sulphuric or nitric, a strong action takes place, accompanied with the disengagement of heat and gaseous substances. The principal product of this reciprocal action, is a new body, having acid properties. During the effervescence which takes place, the mixture has the power of destroying vegetable colours. Carbonic acid is evolved during the decomposition;, and, when the mixture is made in a retort, there comes over a colourless liquid (formic acid), slightly acid, having the

*From Ann. de l' Industrie.

odour of weak acetic acid, and reducing the nitrates of silver or mercury if heated with them.

When nine parts of tartaric acid, and ten parts of chromate of potash are boiled with water, a neutral green liquid is obtained, which being evaporated, does not crystallize, but becomes a brittle green mass. When acetate of lead is added to the solution, a precipitate is formed; which, being well washed, and then carefully decomposed by sulphuric acid, yields a very acid green fluid, uncrystallizable; and, with alkalies, forming either acid greenish-violet coloured salts, or neutral green salts. Cold sulphuric or nitric acids do not act upon this substance; but being heated, they decompose it. When the acid itself is calcined, it yields a green oxide of chrome.

XXXVII.-On an Improvement in Fusing Tallow*. THE Council of Health, at Nantes, has been engaged in an investigation of the best means of fusing tallow, so as to avoid the annoyance which arises from an abundant liberation of stinking vapours, when the ordinary method is used. Much pains have been taken, in acquiring all the information possible, and numerous experiments have been made, both on a large and small scale. The best process which the Council has tried, appears to consist in using, according to M. D'Arcet's suggestion, a certain proportion of sulphuric acid, and operating in close vessels. By the use of the acid, the fumes always evolved, are very much altered, and ameliorated in their smell; and at the same time that the fused tallow is both improved in quality, and increased in quantity, the fusion is very much quickened, and the use of a press dispensed with. By the employment of close vessels, the fumes evolved, can either be conducted to a fire-place to be burnt; or, if that may be thought dangerous, in consequence of the occasional boiling over of the

*From the Ann. de l' Industrie and the Franklin Journal.

melted tallow, they may be conducted into a condensing apparatus, and which is found to condense them readily.

M. D'Arcet uses 100 parts of ctude tallow, cut into small pieces; fifty parts of water, and one part of sulphuric acid sp. gr. 1,848. In some small experiments, a digester was used, having a copper plate pierced full of holes, near the bottom of it, to avoid the necessity of stirring; 1500 parts, (516.5 oz.) of crude tallow, 750 of water, and 124 of oil of vitriol were used, and the fumes conveyed through a pipe into a fire-place, half an hour's ebullition completed the fusion. The infusible matter, when pressed through a cloth, weighed only ninety-six parts, and was slightly acid. The tallow was white, hard, and sonorous, and not acid. Without the acid, the same effect was not produced in an hour.

A tallow-melter tried the experiment with two cwt. of tallow, using the acid, but operating in open vessels; ninety-two per cent. of fused tallow was obtained, and eight of loss occurred. In a second experiment in the large, with acid, only a loss of five per cent. was occasioned. The residuum does not require the use of a press, but it cannot be made into oil-cakes for feeding cattle, unless previously freed from acid by washing it.

Experiments made on condensing the vapours, were found to succeed well, and thus all fear of injury from fire, is avoided. The Council propose conducting the vapours into the drains of the works, and condensing them there; no annoyance being apprehended from the occasional return of the vapours into the building, as that effect can be counteracted, by the use of stink-traps.

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XXXVIII.-On Colza Oil*.

THE following is an extract of a letter from Mr. Thomas G. Clemson Esq. at Paris, to Jacob Green, M.D. professor of chemistry, in Jefferson Medical College, Philadelphia, dated September 18, 1828.

"Dear Sir,-In accordance with the wish which you expressed when you were in Paris, I send you the following remarks, respecting the oil that is burnt through France.

"It is known by the name of Colza oil, Huile de Colza, and is extracted from the seeds of the Brassica Arvensis, or Campestris, a species of cabbage.

"The Colza is very much cultivated throughout France and the Netherlands, on account of its various and useful qualities. In the north of France, and particularly in the environs of Lisle, the greatest possible attention is paid by the farmers to its production. The seed is sown during the month of July, as we sow our seed for the purpose of procuring cabbage plants. They are transplanted in the month of September; a cloudy day being preferred. A man goes first making holes in the earth, at a distance of about twelve inches apart; he is immediately followed by a child, who puts into each hole a single plant; a third person finishes the operation, by closing the earth around the plants with a hoe. When the seed becomes ripe, which generally happens in July of the following year, the plant is cut, tied in small bundles, and put under a shed, or any covered and airy place, to dry. The seeds are then beaten out, and cleaned in the manner of wheat or other grain; and are then treated in the usual manner, for the extraction of their oil. The oil may be used directly it comes from the press, with potash, for the fabrication of soft soap; but if intended for burning, it is necessary that it should undergo a preparation, in order to separate its mucilage and colouring matter, which prevent its ready

*From the Journal of the Franklin Institute.

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