three ounces of acetate of potassa previously dissolved in eight pints of boiling water, and set the whole aside to crystallize, which takes place as the liquor cools, and the acetate of mercury then separates in the form of micaceous crystalline plates, which are to be washed in cold water, and dried on blotting paper. (Edinburgh Pharmacopaia.) In preparing this salt, the quantity of water for dissolving the acetate need not be so large as above directed, one pint being sufficient, but it is necessary to pour the mercurial solution into the acetate. This salt has an acrid taste, and is very difficultly soluble in water, requiring, according to Braconnot, (Annales de Chimie, lxxxvi. 92.) 600 parts of water. It is insoluble in alcohol. It was once used in medicine.

1943. Peracetate of Mercury is formed by digesting the peroxide in acetic acid; it does not crystallize, and affords on evaporation a deliquescent yellow mass, which is decomposed by water into a superperacetate, which remains dissolved; and an insoluble subperacetate.PROUST, Journal de Phys., lvi.

1944. Acetate of Silver is obtained by boiling the acid on oxide of silver, or by mixing solutions of acetate of potassa and nitrate of silver; it forms acicular crystals of an acrid metallic taste.

1945. Acetate of Alumina. This salt is extensively employed by calico-printers as a mordant or basis for fixing colours; they produce it by mixing solutions of alum and acetate of lead: about three pounds of alum are dissolved in eight gallons of water and a pound and a half of sugar of lead stirred into it; a copious formation of sulphate of lead ensues which is allowed to subside, and the clean liquor holding acetate of alumina and a portion of undecomposed alum in solution, is then drawn off, a portion of pearlash and chalk being added to it previous to use, in order to saturate any excess of acid.

Acetate of alumina, formed by digesting recently precipitated alumina in acetic acid, may be procured in deliquescent acicular crystals of an astringent taste, and containing, according to Richter, 73.81 acid + 26.19 alumina: hence it is probably a binacetate.

When acetic acid and alcohol are repeatedly distilled together, a portion of acetic ether is formed, which has a peculiar and agreeable taste and smell, and a specific gravity of about .860 at 60°. It boils at about 160°, is highly inflammable, and emits acetic acid among its products of combustion. This ether is directed in some of the foreign Pharmacopœiæ for medical use, and the following is perhaps the best process for its production. Introduce into a tubulated retort 3 parts of acetate of potassa, 3 of alcohol, and 2 of sulphuric acid, and distil to dryness. To the product add one-fifth its weight of sulphuric acid, and draw off by a gentle heat a quantity of ether equal to that of the alcohol originally employed.

Acetic ether is much more soluble in water than sulphuric ether : according to M. Thenard, water at 60° dissolves about a 7.5 part of its weight, and the solution is permanent. Caustic potassa decomposes it, and forms acetate of potassa.

Oxalic, citric, tartaric, and benzoic acids have been employed in the formation of ethers; the prescence of a mineral acid is indispensable to their formation. - URE's Dictionary, ART. Ether.

1946. THE different sections of this chapter will contain an account of the ultimate and proximate principles of the substances belonging to the animal creation, of the different methods of analysis by which these principles are obtained, and of such of the animal functions as are concerned in their production, where these are susceptible of chemical elucidation.

Nitrogen.

Ammonia.

Carburetted

SECTION I. Of the ultimate Principles of Animal Matter, and of the Products of its destructive Distillation.

1947. THE proximate principles of the animal creation consist, like those of vegetables, of a few elementary substances, which by combination in various proportions, give rise to their numerous varieties. Carbon, hydrogen, oxygen, and nitrogen, are the principal ultimate elements of animal matter; and phosphorus and sulphur are also often contained in it. The presence of nitrogen constitutes the most striking peculiarity of animal, compared with vegetable bodies; but as some vegetables contain nitrogen, so there are also certain animal principles, into the composition of which it does not enter.

1948. The presence of nitrogen stamps a peculiarity upon the products obtained by the destructive distillation of animal matter, and which are characterized by the presence of ammonia, formed by the union of the hydrogen with the nitrogen. It is sometimes so abundantly generated as to be the leading product; thus, when horn, hoofs, or bones, are distilled per se, a quantity of solid carbonate of ammonia, and of the same substance combined with empyreumatic oil, and dissolved in water, are obtained; hence the pharmaceutical preparations called spirit and salt of hartshorn, and Dippel's animal oil. Occasionally the acetic, benzoic, and some other acids are formed by the operation of heat on animal bodies, and these are found united to the ammonia; cyanogen and hydrocyanic acid also frequently occur.

If the gas evolved during the decomposition of animal bodies be examined, it is generally inflammable, and consists of carburetted hybydrogen. drogen, often with a little sulphuretted and phosphuretted hydrogen; carbonic oxide, carbonic acid, and nitrogen, are also sometimes detected in it.

The coal remaining in the retort is commonly very difficult of incineration, a circumstance depending upon the common salt and phosphate of lime, which it usually contains, forming a glaze upon its sur face which defends the carbon from the action of the air. Animal charcoal is also found to be more effectual in destroying colour and smell, than that obtained from vegetables. (387.)

1949. By the term putrefaction we mean the changes which dead Putrefaction. animal matter undergoes, and by which it is slowly resolved into new products. These changes require a due temperature, and the presence of moisture; for below the freezing point of water, or when perfectly dry, it undergoes no alteration.

During putrefaction the parts become soft and flabby, they change in colour, exhale a nauseous and disgusting odour, diminish considerably in weight, and afford several new products, some of which escape in a gaseous form, others run off in a liquid state, and others are contained in the fatty, or earthy residuum.

The presence of air, though not necessary to putrefaction, materially accelerates it, and those gases which contain no oxygen, are very efficient in checking or altogether preventing the process. Carbonic acid also remarkably retards putrefaction; and if boiled meat be care- Antiseptics. fully confined in vessels containing that gas, it remains for a very long time unchanged, as seen in M Appert's method of preserving meat.

There are several substances which, by forming new combinations with animal matter, retard or prevent putrefaction, such as many of the saline and metallic compounds; sugar, alcohol, volatile oils, acetic acid, and many other vegetable substances also stand in the list of antiputrefactives, though their mode of operating is by no means under

stood.

1950. The effluvia which arise from putrescent substances, and more especially those generated in certain putrid disorders, have a tendency to create peculiar diseases, or to give the living body a tendency to produce poisons analogous to themselves. An atmosphere thus tainted by infectious matter, may be rendered harmless by fumigation with the volatile acids, more especially the nitrous and the muriatic; chlorine is also very effectual: the vapour of vinegar, though sometimes useful in covering a bad smell, is not to be relied on. appears evident that the acid and chlorine act chemically upon the pernicious matter, and resolve it into innocuous principles.

It

1951. When muscular flesh is immersed in a stream of running water, it is partially converted into a substance having many of the properties of fat combined with a portion of ammonia. The same changes Adipoure. have been observed where large masses of putrefying animal matter have been heaped together, or where water has had occasional access to it. Nitrate of ammonia is also sometimes formed under the same circumstances.

1952. Instead of considering the proximate principles of animals under separate sections, as has been done in regard to vegetable bodies I shall make them known under the heads of those substances in which they occur, the principal of which are the following:

1. Blood. Albumen. Colouring Matter.

2. Milk. Sugar of Milk.

3. Bile. Resin of Bile.

4. Lymph. Mucus. Synovia, Pus, &c.

5. Urine. Urea. Urinary Calculi.

6. Skin. Membrane.

7. Muscle. Ligament. Horn. Hair.

8. Fat. Spermaceti, &c.

9.

SECTION II. Of the Blood.

1953. In the higher orders of animals the blood is of a red colour. florid in the arteries, and dingy in the veins. The specific gravity of human blood is liable to some variation. I have found it as low as 1.050 and as high as 1.070, but am unable to refer to any circumstances which might be considered as the cause of this difference.

When blood is drawn from its vessels in the living animal, it soon concretes into a jelly-like mass, which afterwards gradually separates into a fluid serum, of a pale straw colour, and a coagulated crassamentum, or cruor, which is red. The cause of this coagulation is quite unknown.

1954. The specific gravity of the serum of the blood, is upon an average 1.030. It reddens the yellow of turmeric, and changes the blue of violets to green, a property derived from a portion of soda. At a temperature of 160°, it becomes a firm yellowish white coagulum, resembling in appearance and properties the coagulated white of egg, and, as the principle to which this property is owing is the same in both substances, it has been called albumen. Alcohol, and many of the acids, also occasion the coagulation of the serum of blood.

100 parts of human serum contain between eight and nine parts of albumen, rather less than one part of carbonate of soda, and about the same quantity of common salt, the remaining 90 parts being water. These at least are the proportions which my own experiments lead me to believe correct; but the analysis is involved in so much difficulty that the results can only be considered as approximating to the truth; indeed it is probable that the composition of the serum is liable to much variation.

Dr. Marcet and Berzelius have each given an analysis of the serum of human blood; the following are their results. (Medico-Chirurgical Transactions, Vol. ii. Annals of Philosophy, Vol. ii.):

1955. Albumen, which constitutes a leading ingredient in the serum, and which we shall presently find also in the cruor, is a very important animal principle, and is found in the greater number of animal fluids and solids.

Liquid Albumen is soluble in water, and always contains a notable portion of soda, indicated by its action on vegetable colours. It is coagulated by heat, acids, and alcohol, unless it be considerably diluted with water, in which case a portion separates in the form of white flakes after some hours' standing. Solution of corrosive sublimate, added to albumen very much diluted, produces a cloudiness, and hence it is a useful test of albumen. (BOSTOCK, NICHOLSON's Journal, xiv.) It is also instantly coagulated by Voltaic electricity; and if two platinum wires connected with a small battery be immersed into a diluted albumen, it will cause a very rapid coagulation at the negative pole, and scarcely any effect at the positive pole. This circumstance induced me to atribute the coagulation to the removal of the alcali, by alcohol, and by acids; but how heat operates is not very obvious, unless we be allowed to consider it as effecting a kind of decomposition of the liquid albumen. We might thus consider liquid albumen as a compound of albumen and soda dissolved in water: the effect of heat would then be to transfer the soda to the water, and thus occasion a coagulation; and a solution of soda is always found oozing from coagulated serum, and has sometimes been called serosity; in time it re-acts upon the coagulum, and dissolves a portion of it.

1956. When albumen is dried in a moderate heat, it shrinks and becomes brown and simi-transparent, resembling horn in appearance and properties. In this state it scarcely dissolves in boiling water, though it gradually softens; it is not prone to decomposition; it dissolves in the alcalis, a portion of ammonia being evolved and a saponaceous compound formed. Dilute nitric acid converts it into a substance having the properties of gelatine. (HATCHETT, Phil. Trans., 1800.)

By destructive distillation albumen furnishes a variety of products characterized by the presence of a large proportion of ammonia. According to Gay-Lussac and Thenard, (Recherches Physico-chymiques) its ultimate constituents are

1

1957. When the coagulum of the blood is carefully washed under a small stream of water, the colouring matter is gradually dissolved, and washed out of it, and a white fibrous substance remains, which has been termed fibrina or coagulable lymph, but of which the chemical properties are those of albumen.

It sometimes happens, when the blood is long in coagulating, as in certain inflammatory diseases, that a portion of this albumen is left without the colouring matter, forming what has been called the buffy coat of blood; in this case it is so tough as to admit of being removed from the coloured portion, and when dried, shrinks up, and appears exactly like horn.