sand, flints, spar, or some other silicious matters. White sand is the substance in the most repute at present, as it requires no preparation for coarse goods; and for the finest, washing in fair water is sufficient whereas flints require a tedious process of calcination, and after that to be pulverized. Many other substances may be used for experiment; though sand only is employed in the manufactory. It is also necessary that the silicious matter should be fused in contact with something called a flux. The substances proper for this purpose are lead, borax, arsenic, nitre, or any alkaline matter. The lead is used in the state of red lead, and the alkalies are soda, pearl-ashes, sea salt, and wood-ashes. When red lead is used alone, it gives the glass a yellow cast, and requires the addition of nitre to correct it. Arsenic, in the same manner, if used in excess, is apt to render the glass milky. For a perfectly transparent glass, the pearl-ashes are found much superior to lead; perhaps better than any other flux, except it be borax, which is too expensive to be used, except for experiments, or for the best looking-glasses. The materials for making glass must first be reduced to powder, which is done in mortars or by horse-mills. After sifting out the coarse parts, the proper proportions of silex and flux are mixed together and put into the calcining furnace, where they are kept in a moderate heat for five or six hours, being frequently stirred about during the process. When taken out the matter is called frit. Frit is easily converted into glass by only pounding it, and vitrifying it in the melting pots of this glass furnace: but in making fine glass it will sometimes require a small addition of flux to the frit to correct any fault. For, as the flux is the most expensive article, the manufacturer will rather put too little at first than otherwise, as he can remedy this defect in the melting pot. The heat in the furnace must be kept up until the glass is brought to a state of perfect fusion; and during this process any scum which arises must be removed by ladles. When the glass is perfectly melted, the glass-blowers commence their operations. The following composition of the ingredients for glass are extracted from the Handmaid to the Arts: For the best flint-glass, 120lbs. of white sand. 50lbs, of red lead, 40lbs. of the best pearlashes, 20lbs, of nitre, and five ounces of magnesia; if a pound or two of arsenic be added, the composition will fuse much quicker, and with a lower temperature. “For a cheaper flint-glass, 120lbs. white sand, 35lbs. of pearl-ashes, 40lbs. red lead, 131bs. of nitre, six pounds of arsenic, and four ounces of magnesia. This requires a long heating to make clear glass; and the heat should be brought on gradualIy, or the arsenic is in danger of subliming before the fusion commences. A still cheaper composition is made by omitting the arsenic in the foregoing, and substituting common sea salt. "For the best German crystal glass, 120lbs. of calcined flints or white sand, the best pearl-ashes 70lbs., saltpetre 10lbs., arsenic half a pound, and five ounces of magnesia. Or, a cheaper composition for the same purpose is, 120lbs. of sand or flints, 46lbs. of pearl-ashes, seven pounds of nitre, six pounds of arsenic, and five ounces of magnesia. This will require a long continuauce in the furnace; as do all others where much of the arsenic is employed. "For looking-glass plates, washed white sand 60lbs., purified pearl-ashes 25lbs., nitre 15lbs., and seven pounds of boras. If properly managed, this glass will be colourless. But if it should be tinged by accident, a trifling quantity of arsenic, and an equal quantity of magnesia, will correct it; an ounce of each may be tried first, and the quantity increased if necessary. "The ingredients for the best crown-glass must be prepared in the same manner as for lookingglasses, and mixed in the following proportions: 60ibs. of white sand, 30lbs. of pearl-ashes, fand 15lbs, of nitre, borax a pound, and half a pound of arsenic. "The composition for common green window. glass is 120lbs. of white sand, 30lbs. of unpurified pearl-ashes,wood-ashes well burnt and sifted 60lbs. common salt 20lbs., and five pounds of arsenic. "Common green bottle-glass is made from 200lbs. of wood-ashes, and 10015s. of sand; or 170lbs, of ashes, 100lbs. of sand, and 50lbs. of the lava of an iron-furnace: these materials must be well mixed." The materials employed in the manufactory of glass, are by chemists reduced to three classes, namely, alkalies, earths, and metallic oxyds. The fixed alkalies may be employed indiffer ently; but soda is preferred in this country. The soda of commerce is usually mixed with common salt, and combined with carbonic acid. It is proper to purify it from both of these foreign bodies before using it. This, however, is seldom done. The earths are silica, lime, and sometimes a little alumina. Silica constitutes the basis of glass. It is employed in the state of fine sand or flints; and sometimes, for making very fine glass, rock crystal is employed. When sand is used, it ought if possible to be perfectly white; for when it is coloured with metallic oxyds, the transparen of the glass is injured. Such sand can only be employed for very coarse glasses. It is necessary to free the sand from all the loose earthy particles with which it may be mixed, which is done by washing it well with water. Lime renders glass less brittle, and enables it to withstand better the action of the atmosphere. It ought in no case to exceed the twentieth part of the silica employed, otherwise it corrodes the glass pots. This indeed may be prevented by throwing a little clay into the melted glass; but in that case a green glass only is obtained. The metallic oxyds employed are the red oyyd of lead or litharge, and the white oxyd of arsenic. The red oxyd of lead, when added in sufficient quantity, enters into fusion with silica, and forms a glass without the addition of any other ingre dient. Five parts of minium and two of silica form a glass of an orange-colour and full of striæ. Its specific gravity is five. The red oxyd of lead renders glass less brittle and more fusible; but, when added beyond a certain proportion, it injures the transparency and the whiteness of glass. The white oxyd of arsenic answers the same purposes with that of lead, but on account of its poisonous qualities it is seldom used. It is cu tomary to add a little nitre to the white oxyd of arsenic, to prevent the heat from reviving it, and rendering it volatile. When added beyond a certain proportion, it renders glass opaque and milky like the dial-plate of a watch. When any com it can be produced by any other means of contagion. For a particular description of this experiment, see the article TRANSFUSION. The analogy existing between the glanders and the venereal disease is exceedingly striking: unluckily, however, they vary in the most essential particular; for the glanders will not yield to mercury. A case indeed occurred at the Veterinary College, of a coach-horse, belonging to Mr. Houlston, one of the examining committee of that institution, supposed to have been perfectly cured by a long course of mercurials. Professor Coleman makes mention of this case in his Lectures, and certainly with good reason, as two facts were apparently established, which seemed to mark it with a degree of decision: these are, first, that the horse was perfectly cured; and, secondly, that the disease of which he was so recovered was the glanders. No doubt would have arisen as to the nature of his disease, had it not yielded to the treatment employed, which was that of repeated and long continued doses of calomel, carried to the extent of salivation. To remove that doubt, however, the horse was kept in a stable with other glandered horses; so that if the disease had been any other than what was supposed, the animal could not fail of being in fected: but the fact was, that he was sent from the infirmary of the College free from the complaint, and we have since had reason to know that he experienced no relapse. It may be supposed, that this case led to many trials of a similar nature, but, unhappily, without the success which was hoped for by the Professor, who exerted his wonted ingenuity to improve the hint which this solitary instance appeared to afford. We too have administered mercury in every way we thought the most promising of success; but, though we have sometimes flattered ourselves that the symptoms were abated by its assistance for a time, we have invariably suffered an ultimate disappointment. Some years ago, great expectations were formed from the use of the mineral acids in the venereal disease, and, from the obvious resemblance that that complaint and the glanders bear towards each other, some trials were made on a few cases of the latter, but without the desired success. We have been informed, and from respectable authority, of horses decidedly glandered recovering spontaneously; but our own experience does not supply a single fact to countenance this suggestion. As the glanders are equally fatal and contagious, great attention ought to be paid to any discharge which may be perceived from the nostrils, or any swelling of the glands; for one of these circumstances does not invariably precede the other. Colds and strangles may be mistaken, by persons unacquainted with the nature of the diseases of horses, for the glanders; but a considerable light will be thrown on the subject, perhaps, by the following observations. In the former complaints there is always some degree of fever, a dulness about the eyes, and a loss of appetite in glanders, none of these symptoms occur, except in its latest stages. In colds, and in the strangles, the swollen glands are painfui to the touch, increase rapidly in bulk, and may be brought without much difficulty to suppuration: in glanders, they are nearly insensibe, and seldom become larger than a walnut. The discharge from a catarrh is usually from both nostrils, is plentiful in quantity, of a healthy colour and consistence, and ineffensive odour; it will flow still more profusely by exposing the head to the steams of hot mashes: on the other band, the discharge in consequence of glanders is originally very small in quantity, soon acquiring a strong and disagreeable smell and colour, and is very little affected by warm vapours. A cold does not always, though it does in general, attack both nostrils: the glanders most frequently affects one only, to which it may confine itself for many months, and the gland will most probably be found enlarged on the side of the affected nostril. In all cases, however, where there appears the most distant prospect of danger, it will be highly prudent to separate the diseased from other horses; and, before the expiration of any long period, we shall be pretty accurately convinced of the real disposition of the complaint. As we are led, by experience and the information of others, to think that severe or tedious catarrh, attended with a discharge from the nose, is sometimes apt to degenerate into glanders, we conceive that, on such an occasion, the means recommended for the cure of the former (see the article CATARRI) should be particularly attended to, as they may possibly have the effect of preventing an evil of a more serious complexion. Wherever the matter may be supposed to be detained or lodged in the upper parts of the nostrils, the steams of scalded bran, and injections of milk-warm water, frequently employed, will be found of considerable advantage. When a horse exhibits such appearances as hold out an undoubted proof of the disease being the glanders, the sooner he is destroyed the safer it will be to the proprietor, as well as more humane to the animal. Nothing but laudable motives of experiment should induce us to protract his tedious and melancholy existence. We have observed, that, whenever a borse is in the least suspected of glanders, it is proper that he should be removed from other horses, and kept alone, sufficiently secure from all possible communication with them: but particular care is also to be taken that the rack, manger, and such other parts of the stable as he may have come in contact with, be thoroughly cleansed from every particle of the infectious matter, the virulence of which we know no means of destroying but by totally removing the matter itself. The most effectual way of accomplishing the above purpose will be by scraping the contaminated parts with knives, or other sharp instruments, scouring them afterwards with soap, sand, and boiling water, and repeating the process till we are convinced it has exterminated every source of contagion; and lastly, a thick coat of well-sized lime should be spread over the whole. It is scarcely necessary to add, that the litter must be swept completely away, and the stable-floor properly cleaned. It is a common practice with the owners of horses, when they have had any one of them seized with the glanders, to bleed and purge the rest by way of prevention: the intention is certainly good, but the consequences cannot possibly prove what they are led to expect. The above method will serve rather to promote, than prevent the disease, as it will considerably increase the action of the absorbent vessels, by which action the glanders is conveyed into the system. All we would recommend on these occasions is, to remove them from that part of the stable in which |