16. The native Americans were more fickly than the Europeans. 17. Men above thirty and thirtyfive years of age, were the hardieft foldiers in the army. Perhaps this was the reason, why the Europeans were more healthy than the native Americans; they were more advanced in life. 18. The troops from Maryland, Virginia, and North Carolina, fick ened for the want of falt provisions. Their ftrength and spirits were only to be restored to them by means of falt bacon. I once faw a private in a Virginia regiment throw away his ration of choice fresh beef, and give feven fhillings and fixpence fpecie for a pound of falt meat. 19. Moft of the fufferings, and mortality in our hofpitals, were occafioned not so much by actual want or fcarcity of any thing, as by the ignorance, negligence, &c. in providing neceffaries for them. After the purveying, and directing apartments were separated (agreeably to the advice of Dr. Monro) in the year 1778, very few of the Ame rican army died in our hospitals. USEFUL USEFUL PROJECTS. Obfervations on the ufe of Acids in bleaching of Linen. By Dr. Eafon. From the foregoing work. The vitriolic acid is that which has univerfally been employed: not because it is preferable to the muriatic acid, but because it was to be bought in large quantities, and at small expence. HE use of acids in bleaching of linen, has been long a known. Formerly milk was chiefly employed; but it had several inconveniences. The quantity requifite could fcarcely be obtained; its effect was flow; and, containing animal matter, it was apt to rot and fpoil the cloth. About thirty years ago it was discovered, that the foffil acids, when properly diluted with water, anfwered much better, and would do more in a few hours, than animal acids could do in a week, in facilitating the whitening of cloth. At firft it was imagined that the mineral acids would be apt to burn er corrode linen substances, when immersed in them. But experience foon difpelled fuch fears, and convinced bleachers, that, by proper management, the danger was next to none. According to the ftrength of the acids, they must be mixed with water, fometimes to feven hundred times their bulk. The nitrous acid, being the most sorrofive, and moft expenfive, has not been used. The muriatic acid being now fold nearly as cheap as the vitriolic, and anfwering in a fuperior degree, will, in a fhort time, I am convinced, be generally adopted by bleachers. As I must confefs my ignorance in the art of bleaching, it may feem prefumptuous in me to hazard a conjecture concerning the manner in which acids act in whitening cloth; but it feems probable, that alkaline falts, which are used in washing out the oil and glutinous parts of flax, on which the green colour depends, depofit an earth in the pores of the cloth. As it is known that acids will alfo diffolve the earthy parts of vegetables, that acid should be preferred which will keep earthy particles fufpended in water. The vitriolic, therefore, is not fo proper; because, with earthy fubftances, it forms immediately a felenite, a fubftance only foluble in a very large quantity of water. This felenitic matter, adhering to the threads of the cloth, will injure it, and make it feel hard to the touch, touch, and probably is the reafon why fome linens wear fo badly. When the muriatic acid is ufed, no felenite is formed. Whatever quantity of earthy matter is diffolv. ed by it, is easily washed out by pure foft water, and the cloth having a foft filky feel, feems to ftrengthen this conjecture. As the muriatic acid is now fold at three-pence per pound, and the common vitriolic acid at four-pence halfpenny; and as the muriatic acid will, in proportion, acidulate a larger quantity of water than the vitriolic, befides the great probability of its anfwering better in whitening of cloth, the bleachers in this part of the world would do well to give it a fair trial. by which the changes, induced by it, are effected in bodies, which are the objects of its action. Within these few years, great changes have taken place in the theory of chemistry. The important difcoveries of Black and Priestley, and of feveral other philofophical chemifts, who have endeavoured to emulate their examples, have happily explained many of the operations of chemistry, which were, before, wholly unintelligible: and the prefent time forms one of the most distinguished æras in the hiftory of that science. We now understand the nature of lime and of alkalis; the difference between a metal and its calx; the cause of the increase of weight in the latter, and of its decrease when returned to a metallic form. The conftitution of atmospheric air has been. demonftrated.-Various gafes, refembling air in many points, but differing from it in others, have been difcovered; and, among thefe, an æthereal fluid, fuperior in its properties to common air, and capable of fupporting life and com buftion more vigorously and durably. Our acquaintance with this pure fluid, which forms the vital part of common air, feems to promife much enlargement to our chemical knowledge, in the inveftigation of its various combinations; and we have already derived much information, relative to the conftitution of the acids, and of water, from the refearches of philofophers into the nature of pure air. Of the gafes which have fo much engaged the attention of the pneumatic chemifts, fixed air, or, as it has more properly been denominated by Sir Torbern Bergman, aërial But though the Hon. Mr. Cavendish had proved the feparation, and afcertained the quantity of this gas, discharged in fermentation, and though Dr. Priestley had early made the above-mentioned obfervations, it does not appear to have occurred to thefe philophers, that this gas was the exciting caufe, as well as the product, of fermentation. It is a fact well known to brewers of malt-liquors, that wort, contrary to what takes place in liquors more purely faccharine, as the juice of the grape, cannot be brought into the vinous fermentation, without the addition of a ferment; for which purpose yeaft or barm, which is a vifcid frothy fubftance, taken from the furface of other maffes of fermenting liquor, has been commonly used. But the nature of this fubftance, much less its mode of action, has not been confidered with that degree of attention, which one would have expected should have been excited by fo extraordinary an agent. We are told indeed, that a vinous ferment induces the vinous, that a ferment of an acetous kind brings on the acetous fermentation, and a putrid one, that fermentation which ends in putrefaction. But we re ceive no more information relative Before I endeavour to deliver any Soon after Dr. Priestley had publifhed his method of impregnating water with fixed air, I began to prepare artificial Pyrmont water, by that means; and early observed that water, fo impregnated, though it at firft fhewed no fparkling when poured into a glafs, yet after it had been kept in a bottle, closely corked, for fome days, exhibited, when opened, the fparkling appearance of the true Pyrmont was ter. ter *. This I attributed, and perhaps not unjustly, to the gas, which had been more intimately combined with the water, and reduced to a kind of latent ftate, recovering its elasticity, and endeavouring to efcape. Having one day made fome punch with this water, and having about a pint of it remaining, after my friends had retired I put it into a bottle, capable of containing a quart, and corked the bottle. On opening it, at the distance of three or four days, the liquor, when poured out, creamed and mantled, like the brifkeft bottled cyder. An old gentleman, to whom I gave a half pint glass full of it, called out in raptures to know what delicious liquor he had been drinking, and earnestly defired that, if I had any more of the fame, I would give him another glafs. Dr. Priestley, as has been already mentioned, had informed us that fixed air, thrown into wine or malt liquer, grown vapid, restored to them their brifknefs and pleasant tafle. On impregnating fome vapid ale with fixed air, I was difappointed in not finding the effect immediately produced. But after bottling the ale, and keeping it clofely stopped for four or five days, it was become as brisk as ale which, in the common way, has been bottled several months. In the year 1778, I impregnated with fixed air a quantity of milk whey, which I had clarified for the purpose of preparing fome fugar of milk, and bottled it. In about a week, the whey in one of the bot tles, which had been fo loosely corked, that the liquor had partly oozed out, was remarkably brifk and sparkling. Another bottle, which was not opened till the fummer of 1782, contained the liquor not in fo brifk a ftate, but become evidently vinous, and without the least acidity, perceptible to the taste. I now began to fufpect that fixed air is the efficient caufe of fermentation; or, in other words, that the properties of yeaft, as a ferment, depend on the fixed air it contains ; and that yeaft is little else than fixed air, enveloped in the mucilaginous parts of the fermenting liquor. I therefore determined to attempt the making of artificial yeast. For this purpose, Í boiled wheatflour and water to the consistence of a thin jelly, and, putting the mixture into the middle part of Nooth's machine, impregnated it with fixed air, of which it imbibed a confiderable quantity. The mixture was then put into a bottle, loosely ftopped, and placed in a moderate heat. The next day the mixture was in a ftate of fermentation, and, by the third day, had acquired fo much of the appearance of yeaft, that I added to it a proper quantity of flour, kneaded the pafte, and after fuffering it to ftand, during five or fix hours, baked it, and the product was bread, tolerably well fer. mented. I now determined to make a more fatisfactory experiment. The wort, obtained from malt, it is known cannot be brought into a state of fermentation, without the aid of a Various methods have fince been devifed of forcing fuch a quantity of gas ta combine, or, at least, to mix, with water, as immediately to communicate to it this appearance. 4 ferment; |