Volume 2

The London medical dictionary; including under distinct heads every branch of medicine ... with whatever relates to medicine in natural philosophy, chemistry, and natural history / By Bartholomew Parr.

Bartholomew Parr

Date:: 1809

Credit: The London medical dictionary; including under distinct heads every branch of medicine ... with whatever relates to medicine in natural philosophy, chemistry, and natural history / By Bartholomew Parr. Source: Wellcome Collection.

734/760 page 724

$iipparent lentor. Its specific gravity is 0.825 at 60“; but it may even be brought to 812. It resists the in- tensest colds hitherto known, evaporates before the point of boiling, which is, however, so low as J6'5°, and, on evaporating, forms a gazeous fluid, leaving a high degice of cold. It mi.xes slowly with water if at rest; Lilt rapidly on shaking, separating numerous bubbles : the united bulk is smaller than that of the separate po:lions, and the specific gravity, of course, greater. Alcohol burns on being touched with an ignited body : and the flame is pale blue on tlie outside, though white in the centre. Salts of copper render the flame of a beautiful emerald green, borax a greenish yellow, nitre a dun yellow, and the soluble salts of stronlian a deep blood red. The strongest alcohol is consumed so per- fectly as to inflame gunpowder, if jilaced at the bottom ot the vessel in which it burns. When alcohol has burnt away on cotton, and inflames it, chemists call ]t rectified spirit of wine. Equal measures of this rec- tified spirit and of pure water form spiriti/s vini tcnnior, proof spirit. If to the rectified spirit as much well dried and jet warm alkaline salt be added as that a part of it lemains undissolved at the bottom, it will absorb the remaining aqueous humidity, and the spirit may be poured from its surfiice. After which, if a little cal- cined vitriol or burnt alum be added to this dbphlegni- ated spirit, and it be again distilled, it will arise pure either superfluous phlegm, or any of the a kaline salt that may be detained in it. This is called alcohol. Ihe college of physicians direct the followinir proce.ss ; lake of rectified spirit of wine, one gallon; kail made hot, one pound and a half; pure kali, one ounce; miy the spirit with the pure kali, and after- wards add one pound of the hot kali: shake them, and digest for twenty-four hours. Pour off the spirit, to which add the rest of the kali, and distil in a water- bath. It is to be kept in, a vessel well stopped. The specific gravity of the-best alcohol is to that of distilled ■water as 815 to iot.0. Eut, as we have said, it may be lendered still stronger. An empyreumatic flavour, how- e\er, often remains from the first incautious distillation, and a fetid oil, from an accidental or a designed impreg- nation. The former disappears by age, especially if the ^splrlt be kept in chai red casks; but the oil is seldom se- parated. It may be discovered by rubbing some of the spiiit on the palm of the hand. Alkalis and lime, with a subsequent distillation, remove it; but a portion of the spirit is in this way decomposed. Baume, who thinks this oil more common when the spirit is pre- pared from the rich Spanish wines, found that the first product of tile distillation was not oily, and on this ob- servation founded his process of purifying. This was o distil the spirit succe.ssively, reserving all the first portions, then to mix them and distil off one half, fiscal operations have rendered it a problem of pecu- lar advantage to ascertain the comparative strength of different spirits. Shaking the fluid, and marking the period at which the bubbles disappear, becomes, from habit, a good test of its strength ; but art will supply the means of imitating what has been attributed to the propoilion of alcohol. The quantity of water left after burning is a better criterion. Good rectified spi- rit should leave about 0,25, French brandy 0.50, com- mon malt .spirit 0.05. Another test is the quantity of water which good dry carbonat of potash carries down. and one usually employed of rum is its swimmino' in olive oil; but all are liable to objections, and the most certain means of ascertaining the proportion of alcohol m a given quantity of spirit, is by ascertaining its spc- ajic gravity. The immense and minute labours of sir Char es Elagden and Mr. Gilpin on these subjects may be found in the seventy-ninth and eighty-second volumes of the Philosophical Transactions; but, though we think a more minute attention to the strength of spirits in pharmaceutical processes highly desirable the disquisition is by far too remote from our present object to detain us. The complicated circumstances in this inquiry afford many curious subjects of hydrometri- cal investigation, which to a philosophic mind must b'* highly interesting. It appears, in general, that the greatest diminution in bulk, or concentration, in pro- portion to the quantity of ingredients, which takes place between alcohol and water, occurs, when equal bulks of each are used, being more than y^th of the whole. But the greatest possible diminution, obtaina- ble by any admixture of water, happens when two parts of the latter are added to one of alcohol, bein-r fi.81 parts where one hundred of alcohol are employed'^ This last is the highest term of actual diminution, L it is again less than O'.Sl in one hundred, if still more water is added. Alcohol has been analysed in a variety of waj'S; but we have not hitherto attained greater accuracy^han from the experiments of Lavoisier, who concluded that one hundred parts of alcohol contained of water; 28.53 of carbone; and 7.&7 of hydrogen. In the strongest alcohol, water already formed probably exceeds one-half its weight, which in burning is carried off by evaporation. Pure alkalis are soluble in alcohol; but carbonated alkalis only attract the water. The solution is of a high red brown colour, and recommended as a resolvent by Van Helmont, under the appellation of thicturatartari. The proportion of pure alkali, dissolved by the strong- est alcohol, is about 0.187 of its weight; but, as al- ready hinted, the spirit is in part decomposed; for the alkali attracts the carbone, and rhoraboidal or spicular crystals are deposited. If this solution is repeatedly distilled, the whole spirit is decomposed, leaving carbo- nat and acetite of potash. Lime has a similar effect. Pure ammonia dissolves in alcohol, and the carbonated ammonia to a certain extent, especially by means of distillation. When alcohol, however, is added to a sa- turated solution of ammonia, in water the latter is pre- cipitated in confused crystals, called uffa Helmontii. 'I'he action of the stronger acids has been already noticed in the article Ether, q. v.; and the weaker ones dissolve in it or decompose it imperfectly. Howard’s )ulininatiii<r inercury is procured by means of alcohol, which, when digested with nitrat of mercury, is decomposed, and be- comes the oxalat of this metal, in which state it fulmi- nates. 'I he other neutrals are dissolved by alcohol, with different degrees of affinity, and it lurnishesa ready me- thod of approximating the saline contents of mineral waters. Lavoisier found that pure spirit did not dissolve carbonated or sulphurated soda, sulphurated or min iated magnesia, or even common salt. When mixed with halt its weight of water, it dissolved a considerable quantity of common salt; but sulphat of soda was not dissolved in any mi.\ture in which the quantity of spirit$