265 Figure of metallic Money.-Bleaching of Impreffions from Engravings. bination of both methods is neceffary. If a coin be ftruck with indentations or parts depreffed beneath the common furface, and in thefe there be prominent objects or defigns, not more elevated than that furface, the general advantage, with regard to wear, will approach towards that of the plain surface itself, and the impreffion will be at leaft as difficult to imitate, if not more so than that of a defign rifing totally above the common furface *. The late copper coinage of pieces of one and of two pennies are of this kindt. To fum up the foregoing conclufions in a few words, we may remark, that, 1. The State is unable (from the natural impracticability of the thing) to appoint two diftinct articles of commerce as the circulating mediums of exchange. 2. The measure of value or legal tender ought to confift in the metal which bears the highest price, namely, gold. 3. Coin of filver and copper are required for fmaller fractions than the actual fubdivifions of the gold coin, but should be optional in the receipt for any larger fums. 4. These laft-mentioned coins ought to represent a value in gold equal to their own quantity of metal, at the highest (or perhaps medium) market price added to the charge of fabrication. 5. No fufficient reafon has yet been given, to shew that the standard of gold coin should be changed in order to render it more durable. 6s The beft figure of coin is a fhort cylinder or flat round plate; and 7. The distinctive marks or impreffions fhould be made neither altogether hollow nor altogether in relief, but by a combination of both forms, fo as to leave a flat bearing furface on each fide. V. An eafy Method of cleaning and bleaching Copper-Plate Impressions or Prints. Extracted from a SINCE INCE the happy invention of engraving in copper, which no doubt owes its origin to the revival of the art of chafing and ornamenting plate, collectors have availed themselves of this means to accumulate and preferve copies of the most valuable pictures and drawings. This object of research becomes every day more prevalent, and prints of the early and most celebrated masters are now fought for with the utmost avidity. Ancient prints are valuable, not only for their own intrinfic merits, but as monuments of *Few coins have been made of this figure. The Chinese coin of mixed copper called the cafh is the most remarkable, and perhaps the only one of extenfive circulation. + Of copper, by M. Boulton, Efq. for Government. The penny is rather more than 1.4 inch in diameter, and about 0.13 inch thick at the edge, and weighs 1 oz. avoirdupois. A circular part of the face on each fide rather more than 1.1 inch in diameter is depreffed by the stroke of the dye, in one of which is feen the head of the King in relief, and in the other a figure of Britannia. Upon the prominent rim on one fide are the words "Georgius III. D. G. Rex," and on the other "Britannia 1797" in funken letters. The edge or cylindrical furface is plain. The two-penny piece resembles the penny; but its diameter is 1.4 inch : funk face 1.25 inch, and weight 2 oz. avoirdupois wanting 20 grains in the piece before me. I fuppofe the average weight to be 2 ounces. Tranflated from the Italian. Communicated by Andrew Duncan, jun. M. D. of Edinburgh, who received it from the author. The original is inferted in the Giornale Letterario di Napoli, No. 85. M m VOL. II.-SEPT. 1793. the the hiftory of the art. But their scarcity renders them ftill more valuable. Most of thofe which are ftiil extant are defaced by negligence, during the time of their remaining fufpended against walls expofed to smoke, vapor, and the excrements of infects. Collectors of prints have not, however, fhewn the fame partiality as antiquarians for the patina; but on the contrary they have fought and practifed a method of clearing prints from thefe impurities. This method confifts in fimple washing with clear water, or a ley made of the afhes of vine stalks or reeds, and laftly by a long exposure to the dew. Aqua fortis is also used for the fame purpose, but with a degree of rifque at least equal to its advantages. The ley diffolves not only the impurities but likewife the oil of the printing ink, and either discharges it totally, or leaves a cloudy appearance. The aqua fortis acts on the vegetable fibre, of which the paper itself is compofed, and produces a dark colour, which cannot be removed by means of this liquid, but by an action which would confiderably injure the paper itself. The discovery of Priestley, of the fluid erroneously named by him, but fince known by the name of oxygen; and the information we have obtained from Scheele, of the effects of its combination with muriatic acid, have led Berthollet to the useful application of its properties to the act of bleaching cloths, Chaptal to that of bleaching prints and books, and Giobert to the art of painting. But the method of making this preparation is too inconvenient for a mere amateur and collector of prints, and the oxygenated muriatic acid is not yet to be purchafed ready prepared in Italy. It may not, therefore, be unacceptable to describe an easy method of effecting this purpose without the difficulties of chemical processes, and within the ability of any person to perform. It is known that oxygen is abundantly contained in the combinations called metallic calces, though in a state of inactivity; and it is equally well afcertained, that these substances have a very strong attraction for it. On the other hand it is a fact, that fome of the metallic calces of very moderate price are capable of eafily yielding the whole or the greateft proportion of this conftituent part. Manganefe is not very well adapted for this purpose ; but minium is much better. Nothing more is required to be done, but to provide a certain quantity of the common muriatic acid, for example, three ounces, in a glass bottle, with a ground ftopper, of such a capacity that it may be only half full. Half an ounce of minium muft then be added; immediately after which the ftopper is to be put in, and the bottle fet in a cold and dark place. The heat, which foon becomes perceptible, fhews the beginning of the new combination. The minium abandons the greatest part of its oxygen with which the fluid remains impregnated, at the fame time that it acquires a fine golden yellow, and emits the deteftable fmell of oxygenated muriatic acid. It contains a fmall portion of muriate of lead; but this is not at all noxious in the fubfequent procefs. It is alfo neceffary to be obferved, that the bottle must be ftrong, and the ftopper not too firmly fixed, otherwife the active elaftic vapor might burft it. The method of ufing this prepared acid is as follows: Provide a fufficiently large plate of glafs, upon which one or more prints may be feparately spread out. Near the ed es let there be raised a border of foft white wax half an inch high, adhering well to the glass and flat at top. In this kind of trough the print is to be placed in a bath of fresh urine, or water containing a fmall quantity of ox gall, and kept in this fituation for three or four hours. The fluid is then to be decanted off, and pure warm water poured on, which must be changed every three or four hours until it paffes limpid and clear. water. Bleaching of Prints.-Curious Facts refpecting the Zebra. 267 clear. The impurities are fometimes of a refinous nature, and refift the action of pure When this is the cafe the washed print must be left to dry, and alcohol is then to be poured on and left for a time. After the print is thus cleaned, and all the moisture drained off, the muriatic acid prepared with minium is to be poured on in fufficient quantity to cover the print; immediately after which another plate of glafs is to be laid in contact with the rim of wax, in order to prevent the inconvenient exhalation of the oxygenated acid. In this fituation the yelloweft print will be feen to recover its original whiteness in a very short time. One or two hours are fufficient to produce the defired effect; but the print will receive no injury if it be left in the acid for a whole night. Nothing more is neceffary to complete the work, than to decant off the remaining acid, and wash away every trace of acidity by repeated affufions of pure water. The print being then left to dry (in the fun if poffible) will be found white, clear, firm, and in no refpect damaged either in the texture of the paper or the tone and appearance of the impreffion. AN VI. On the Propagation of the Zebra with the Afs ↑. experiment was made in the year 1773 with a zebra, in the collection of the late Lord Clive, the result of which, though of confiderable interest to the natural historian, is no where upon record in any public journal or printed work. A fet of questions were propofed at the time of the event to Mr. Parker by Sir Jofeph Banks; which, together with the answers, he has at my request permitted me to make use of. The zebra was first covered by an Arabian horfe. For this purpose it was found neceffary to bind her, and she shewed great difguft. As fhe did not conceive, an English ass was procured; to which the shewed a degree of averfion, scarcely if at all less than to the horse, and was fubjected to him by the same means. The refult of this trial not being more favourable than the other, recourfe was had to the extraordinary expedient of painting another ass fo as to refemble the zebra. Complete fuccefs attended this deception. When the animals were put together, the zebra at first appeared shy; but fhe received the embraces of the painted afs, and conceived. The offspring was a fine large male foal, which was just turned of fix months old at the time of enquiry, namely, December 1773. It refembled both parents; the father as to make, and the mother as to colour; but the colour was not fo ftrong, and the stripes on the shoulders were more confpicuous than on any other part. In answer to a question directed to that object, the relator ftates it as his opinion, that it would very probably propagate its species, as it did not appear at all like a mule. In the course of the year after this information was received, his lordship died fuddenly, and * As I have not repeated this precess, I cannot eftimate how far the presence of the lead may weaken the corrofive action of the acid on the paper; but I should be difpofed to recommend a previous dilution of the acid with water. Whoever ufes this process will of course make himself master of the proportion of water required to dilute the acid, by making his first trials with an old print of no value. N. + Communicated by the Right Hon. Sir Jofeph Banks, Bart. K. B. P. R. S. &c. &c. He was either Steward or in fome other confidential employ to Lord Clive. the collection of animals was difpofed of. Sir Jofeph Banks was then abfent from town; and upon his return he was prevented, by this circumftance, either from purchafing the animals or acquiring any further information refpecting the foal. I have lately endeavoured to obtain fome intelligence on this behalf among the dealers in animals, but hitherto without fuccefs. VII. On the Proces of Bleaching with the Oxygenated Muriatic Acid; and a Defcription of a new Apparatus for Bleaching Cloths with that Acid diffolved in Water without the Addition of Alkali. By THEOPHILUS LEWIS RUPP*. THE arts which fupply the luxuries, conveniences and neceffaries of life have derived but little advantage from philofophers. A view of the hiftory of arts will evince the justice of this obfervation. In mechanics, for inftance, we find that the most important inventions and improvements have been made, not through the reasonings of philofophers, but through the ingenuity of artists, and not unfrequently by common workmen. The chemist in particular, if we except the pharmaceutical laboratory, has but little claim on the arts on the contrary, he is indebted to them for the greatest discoveries, and a prodigious number of facts, which form the bafis of his science. In the discovery of the art of making bread, of the vinous and acetous fermentations, of tanning, of working ores and metals, of making glass and foap, of the action and applications of manures, and in numberless other difcoveries of the highest importance, though they are all chemical proceffes, the chemift has no share. But no branch of the useful arts is lefs indebted to him than that of changing the colours of fubftances. The art of dyeing has attained a high degree of perfection without the aid of the chemift, who is totally ignorant of the rationale of many of its procefles, and the little he knows of this subject is of a late date. The process of dyeing the Turkey red has been known and practised from time immemorial by the most uncultivated nations, but its theory is notyet understood by philofophers. The manufacture of indigo and its application have been long known to the planter and the dyer; but it is not more than ten years fince a true theory of them has been formed. The art of printing or topical dyeing is of the greatest antiquity; but the theory of this procefs, and of adjective colours in plain dyeing, was unknown till Mr. Henry developed it in the Memoirs of this Society t. The bleaching or whitening of vegetable substances has been long practised; but the knowledge of its theory could not be antecedent to the æra of pneumatic chemistry. We might even at this moment have been unacquainted with the cause of the deftruction of the colouring matter of vegetable fubftances, if the difcovery of the oxygenated muriatic acid, and its effects on colouring matter, had not pointed it out to us. For this discovery, and its inestimable advantages, the arts are indebted to the juftly celebrated Scheele; and I am happy to pay this tribute to chemistry after the mortifying truths which I have ftated above. M. Berthollet loft no time in applying the properties of this curious and highly interesting substance to the most important practical ufes. His experiments on bleaching with the oxygenated muriatic acid proved completely fuccefsful, and he did not delay to communi+ Manchester Memoirs, vol. iii. Manchester Memoirs, vol. v. part i. cate Improved Process of Bleaching. 269 cate bis valuable labours to the public. The new method of bleaching was quickly and fuccefsfully introduced into the manufactures of Manchester, Glasgow, Rouen, Valenciennes, and Courtray; and it has fince been generally adopted in Great Britain, Ireland, France, and Germany. The advantages which refult from this method, which accelerates the process of whitening cottons, linens, paper, &c. to a really furprifing degree in every season of the year, can be justly appreciated by commercial people only, who experience its beneficial effects in many ways, but particularly in the quick circulation of their capitals. Great difficulties for a time impeded its progrefs, arifing chiefly from prejudice and the ignorance of bleachers in chemical proceffes. Thefe obftacles were, however, foon removed by Mr. Watt at Glasgow, and by Mr. Henry and Mr. Cooper at Manchefter. Another difficulty prefented itself, which had nearly proved fatal to the fuccefs of the operation. This was the want of a proper apparatus, not for making the acid and combining it with water (for this had been fupplied in a very ingenious manner by Mr. Watt and Mr. Berthollet *), but for the purpose of immerfing and bleaching goods in the liquor. The volatility of this acid, and its fuffocating vapours, prevented its application in the way commonly used in dyehoufes. Large cifterns were therefore conftructed, in which pieces of stuff were ftratified s and the liquor being poured on them, the cifterns were clofed with lids. But this method was foon found to be defective, as the liquor could not be equally diffufed; the pieces were therefore only partially bleached, being white in fome parts and more or lefs coloured in others. Various other contrivances were tried without fuccefs, till it was discovered that an addition of alkali to the liquor deprived it of its fuffocating effects without deftroying its bleaching powers. The process began then to be carried on in open veffels, and has been continued in this manner to the prefent period. The bleacher is now able to work his pieces in the liquor, and to expofe every part of them to its action without inconvenience. This advantage is unquestionably great; but it is diminished by the heavy expence of the alkali, which is entirely loft. It is moreover to be feared, that the alkali which is added to the liquor, though it does not deftroy its power of bleaching, may diminish it; becaufe a folution of the oxygenated muriat of potash, which differs from the alkaline bleaching liquor in nothing but in the proportion of alkali, will not bleach at all. This is a well-known fact; from which we might infer, that the oxygenated muriatic acid will lofe its power of deftroying the colouring matter of vegetable substances in proportion as it becomes neutralized by an M. Berthollet's apparatus, however, is too complex for the use of a manufactory; Mr. Watt's is better; but a range of four, five or fix hogfheads or rum puncheons connected with one another in the manner of Woulfe's diftilling apparatus is preferable to either of thein. Agitators on M. Berthollet's principle may be applied. The retort or matrafs fhould be of lead, ftanding in a water bath; its neck should be of fufficient length to condense the common muriatic acid, which always comes over; and it should form an inclination towards the body of the retort, fo that the condensed acid may return into it. I beg leave to observe here, that I always found the liquor to be strongest when the diftillation was carried on very flowly. I have alfo found that the strength of the liquor is much increased by diluting the vitriolic acid more than is ufually done. The following proportions afforded the strongest liquor: Three parts manganefe. The proportion of manganefe is fubject to variation according to its quality. alkali. |