gases subjected to different pressures are not equal, but diffe materially from each other. It is evident also that the ratio between the specific heats is not that of the densities; for the ratio of the pressures to which the air in these experiments was subjected is 1:1-3583, obviously different from that of the specific heats 1: 1.2396.

If we attend to the weight, it results, from the same experiments, that the specific heat of a mass of air increases with its bulk, without being proportional to it.

The experiments on the different gases having been made under different pressures, it was necessary, to make them capable of being compared together, to reduce the results to what they would have been supposing them all made under the same pressure. The experiments described in this section furnished us with the means of making this correction; for since we know that an augmentation of pressure, in the ratio of 1 to 1.3583, increases the specific heat of the same volume of air in the ratio of 1 to 1.2396, we may deduce from these ratios that of the specific heats of two equal volumes of air subjected to pressures of a different ratio from those that have been stated. We without running the risk of committing an error of any great importance, employ for that purpose the following proportion: (1.3583 1 = 0·3583): (1.2396 1= 0.2396) ::

D

I

1

may,

); in which D and P denote the two

different pressures; c, the known specific heat, corresponding to the pressure P; and x, the specific heat sought, corresponding to the pressure D. This formula is founded on the supposition that the differences of the corresponding pressures, which may be considered as true when the question relates to small differences. We employed the same formula for all the gases, because the law, according to which their specific heats vary according to different pressures, if it be not the same for all, must, at least, be very nearly the same.

(To be continued.)

ARTICLE X.

General Views of the Composition of Animal Fluids. By J. Berzelius, M. D. Professor of Chemistry in the College of Medicine at Stockholm.

(Continued from p. 208.)
Of Bile.

It is well known that the elder chemists considered the bile as an animal soap composed of soda and a resin. The accuracy of

this opinion had often been questioned, owing to the very small proportion of soda; and lately our skilful contemporary, Thenard, has published an analysis of bile, in which he gives as its component parts, soda, a peculiar matter named by him Picromel, and a resin, which, united, produce a fluid that has the taste and other distinguishing properties of this secretion. Nevertheless, I am convinced that there is no such resin as Thenard and his predecessors have described. I shall not here relate my experiments on this supposed resin in particular, but shall give the result of my inquiries on the bile itself, which will enable the reader to confirm or reject my opinions, according as he finds them founded on accurate experiment.

The substance which is peculiar to bile has an excessively bitter taste followed by some sweetness; the smell is also peculiar, and the colour in most animals varies from green to greenish yellow. It is soluble in water, and its solubility is not in the least promoted by the alkali of bile, since, when this is neutralized by any acid, the peculiar matter does not separate: it also dissolves in alcohol in all proportions. Like the albuminous materials of the blood of which this peculiar matter is composed, it will unite with acids, producing compounds of two degrees of saturation, and hence, of solubility. The acetous acid, which gives soluble compounds with the albumen of the blood, does the same with the peculiar matter of the bile; and hence this matter is not precipitated on adding this acid to bile, though it falls down on the addition of the sulphuric, nitric, or muriatic acids. It is this sparingly soluble compound of biliary matter with a mineral acid which has been mistaken by many chemists for a resin; since it possesses the external characters of a resin, melts when heated, dissolves in spirit of wine, and is again precipitated (in part at least) by the addition of water. The alkalies, alkaline earths, and alkaline acetates, decompose and dissolve it: the former by depriving it of its combined acid; the latter, by furnishing it with acetous acid, which renders it soluble in

water.

The peculiar matter of bile will also combine with many metallic oxides into a pulverulent mass; and the above described resiniform compound of this matter, and any of the mineral acids, often form with the same oxides a substance like a plaster, resembling in this respect also the true resins.

The degree of insolubility possessed by these compounds of acid and biliary albumen varies both according to the species of animals, and also according to the length of time that the bile has been extracted; for the longer it has been kept, the more solubility these compounds acquire; but in this case I have always found that by pouring in a fresh quantity of acid, and slowly evaporating the mixture, the resinous matter falls down as the supernatant liquor becomes more acid.

The biliary matter may be obtained pure in the following way; mix fresh bile with sulphuric acid diluted with three or four times its weight of water; a yellow precipitate of a peculiar nature first appears, which must be allowed to subside and be removed; then continue to add fresh acid as long as any precipitate is formed; beat the mixture gently for some hours, and afterwards decant the fluid part, and thoroughly edulcorate the green resin which is left. This resin reddens litmus, and is partially and sparingly soluble in water. It may be deprived of its acid in two ways: one of them is by digesting it with carbonate of barytes and water, whereby the carbonate is decomposed, and the water forms a green solution possessing all the peculiar characters of bile: the other way is by dissolving it in alcohol, and digesting the solution, either with carbonate of potash, or carbonate of lime, till it no longer reddens litmus, and then evaporating it to dryness. Either of these methods will give the pure biliary matter, and there are also other ways of obtaining it, which I have described in my work on Animal Chemistry, vol. ii. p. 47.

This peculiar biliary matter, when pure, resembles exactly entire desiccated bile. Being soluble in alcohol it might be supposed that it would dissolve in ether; but this is not the case; for ether only changes it to a very fetid adipocirous substance, exactly as it acts upon the albuminous matter of the blood. One circumstance relating to the biliary matter has much surprised me, which is, that it gives no ammonia by destructive distillation. Therefore it contains no azote; but what can have become of the azote of the albuminous matter of the blood? for no vestige of azote is found in any other of the constituent parts of the bile, nor does bile contain any ammonia.

The following is the result of my analysis of bile:

Water...

Biliary matter...

Mucus of the gall bladder, dissolved in the bile
Alkalies and salts (common to all secreted fluids)

907.4

80.0

3.0

9.6

1000'0

2. The Saliva.

The saliva is one of the fluid secretions which contain more water than the blood. When first discharged from the mouth it holds suspended a mucus which is not dissolved in the saliva; but gives it its frothy quality. This mucus gradually subsides from the saliva when kept in a cylindrical vessel, and with more ease when previously diluted, after which the supernatant saliva may be decanted off.

Saliva is composed of

Two of these ingredients require further notice.

The peculiar animal matter of the saliva is obtained by adding spirit of wine to dried saliva, which dissolves the muriates, lactates, &c. The soda which remains in the insoluble portion is then extracted by fresh spirits slightly acidulated with acetous acid. The residue is mucus mixed with the peculiar salivary matter, which last may be dissolved by water, leaving behind the insoluble mucus.

1

This peculiar matter is therefore soluble in water, but not in spirits of wine. The solution in water, when evaporated to dryness, leaves a transparent mass that easily again dissolves in cold water. This solution is not precipitated either by alkalies, or acids, or subacetate of lead, or muriate of mercury, or tannin; neither does it become turbid by boiling.

The mucus of the saliva is readily procured by mixing saliva with distilled water, from which the mucus gradually subsides, and it may then be collected on the filter and washed. In this state it is white, and would seem to contain phosphate of lime mixed with it. This mucus is quite insoluble in water; it becomes transparent and horny in the acetic, sulphuric, and muriatic acids, but does not dissolve in them, and the alkalies separate nothing from them. The mucus therefore contains no earthy phosphate, though its appearance would lead to suspect this earthy salt. It dissolves in caustic alkali, and is again separated from it by the acids. A small proportion escapes the action of the alkali, but yields to muriatic acid, and is not separable from this acid by an excess of alkali. The mucus of the saliva is very easily incinerated, and though no phosphate of lime is detected in it by the acids in its natural state, a considerable portion of phosphate appears in the ash after combustion.

Is this mucus secreted in the salivary glands, or is it only the common mucus of the mouth? The latter appears most probable, though I confess that the large quantity of this mucus contained in the saliva, and the great difference between its chemical properties and those of the pasal mucus, throw some doubt on this opinion.

It is this mucus that produces the tartar of the teeth, which at first is only mucus precipitated on the surface of the teeth and

adhering to them, but soon it begins to decompose, its colour changes by the influence of the air from white to yellow or greenish, the warmth and moisture of the mouth contribute to complete the decomposition, and the same earthy phosphates which are produced by oxidation and combustion in open fire are here formed and slowly deposited on the surface of the tooth by a slower but a similar process. The tartar is, therefore, as it were, the ash of mucus crystallized on the tooth, and this, as is well known, will in length of time form very large incrustations. I have found it to consist of the following substances: —

3. The Mucus of the mucous Membranes.

I shall premise some remarks on the term mucus, as applied to animal chemistry. It properly signifies the mucus of the nostrils; but many chemists have extended it to other substances found in the animal fluids; so that Jordan, Bostock, Haldat, and others, reckon it among the constituents of these fluids. None of these chemists has considered mucus, used as a general term, as identical with the nasal mucus, or, if they have thought so, it has been a very great error. I must now mention that there is no such principle as the mucus of animal fluids, the substance so considered being in reality lactate of soda mixed with the animal matter that always accompanies it: but if it did exist as a separate principle, some other term should have been used, to distinguish it from the mucus of the nostrils, which is very different.

The chemists who have the most attended to the analysis of mucus have been Messrs. Bostock, Fourcroy, and Vauquelin; but none has given a very satisfactory account of its properties. The two latter chemists, who have published a long memoir on animal mucus, have too much generalized the characters peculiar to nasal mucus, in attempting to extend them to the mucus of the intestines and gall bladder, for example, where they are totally inapplicable.

The mucus of mucous membranes is produced from the same secretory organ throughout the body, and possesses every where the same external characters which constitute mucus: but in chemical properties the mucus of different organs varies considerably, according to the required use in protecting these organs from the contact of foreign substances. Thus the mucus of the nostrils and trachea, which is intended to protect these mem