position of the solid droppings of different animals, which must affect the nature of the smells they severally emit. Thus man discharges through his kidneys a large proportion of the phosphorus contained in the food he eats; while the cow, the horse, and the sheep, emit none of it in this way. All the phosphorus which these animals cat, therefore, is rejected in their solid droppings; and inasmuch as the compounds of phosphorus, which are formed in decaying animal and vegetable substances, are generally distinguished by peculiar and offensive smells, it is easy to understand that the droppings of these animals, when they heat and ferment, must emit some-more or less nauseous, and probably injurious-odours, which are not to be recognised in similarly fermenting nightsoil.

CHAPTER XXVII.

THE SMELLS WE DISLIKE.

SMELLS PRODUCED BY CHEMICAL ART.

Smells produced by chemical art.-Seleniuretted hydrogen.-Phosphuretted hydrogen. Mercaptan.-Kakodyle.-Alkarsin.-Cyanide of Kakodyle.-Compounds of tellurium.-Interesting chemical relation between sweet odours and stinks.Acrolein.-Offensive substances produced by destructive distillation.--Smells emitted by manufactories.-The sulphuric acid, soap, candle, vinegar, and glass makers.-Lead and copper smelters.-Such smells may and ought to be prevented.

V. SMELLS PRODUCED BY CHEMICAL ART.-In the preceding chapter, I have mentioned incidentally, that, though many natural smells are very offensive, yet that we can already produce others by art which are still more so. Indeed, were any useful purpose to be served by them, we could, by familar chemical processes, add stenches almost inconceivably disgusting to those which have hitherto been prepared. A reference to a few only of those which are now well known in our laboratories, will satisfy the reader as to the resources of the chemist in the production of stenches.

1o. Seleniuretted Hydrogen.-We have seen that sulphur is a substance which forms many combinations distinguished by their disagreeable odours; and of these I

have described sulphuretted hydrogen as one which both occurs in nature, and can be easily produced by chemical

art.

Selenium is an elementary body which, though less abundant in nature than sulphur, resembles it very much in sensible and chemical properties. Like sulphur, it also combines with hydrogen, and forms a poisonous gas-the seleniuretted hydrogen. But this gas greatly exceeds the sulphuretted hydrogen, both in its evil smell, and in its noxious qualities. A single bubble of it allowed to escape into the air of a room, produces on those who breathe it all the usual symptoms of a severe cold and affection of the throat, and these symptoms do not pass off for several days. The singular virulence of this substance illustrates in a very striking manner the injurious influence which may be exercised over the health of the people by the presence of very minute portions of foreign bodies in the air we breathe.

2°. Phosphuretted Hydrogen is a gas in which phosphorus takes the place of the sulphur and selenium contained in the two gases above mentioned. It is easily prepared in the laboratory, and is possessed of a peculiarly fetid smell. It is one of the compounds of phosphorus also, which is naturally produced, along with other disagreeable substances, during the decay of animal bodies, and contributes to the repulsive character of the smells which decaying animal matter gives off.

The two metals, arsenic and tellurium, also combine with hydrogen, and form gaseous compounds-the arsenietted and telluretted hydrogens. These gases are of so fetid a kind that chemists rarely venture to prepare them; and when they do so, it is only after taking careful precautions against their escape into the air of the room in which the experiments are made.

It is a common character, also, of all the five gases I

have named, that they combine with other compound bodies, and especially with organic compounds, producing new substances far more fetid than themselves, and possessed of stenches which cannot be described in words. To this class belong some of the following compounds :—

3°. Mercaptan.-Among organic substances of much importance in modern chemistry is a class of bodies to which the name of compound radicals is given. These bodies consist of two or more simple substances united together, and are therefore compound bodies; and yet behave, in many respects, as if they were themselves simple. To this class of bodies belong those which I have had occasion to mention under the names of

Among other properties which these compound radicals possess is that of combining with sulphur, and of forming with it new combinations of an extremely fetid character. Of this the sulphureous oils of garlic and assafoetida are natural examples.

When ethyle is combined artificially with sulphur, it forms what is called sulphuret of ethyle, and when this again is combined with sulphuretted hydrogen, it forms mercaptan. This latter substance is a colourless volatile liquid, possessed of a most offensive, penetrating, and concentrated odour of onions, which adheres obstinately to the hair and clothes. It is, in fact, an artificial oil of garlic,

doms.

By organic is meant such as are derived from the animal or vegetable king

That is, like the simple substances-hydrogen, chlorine, the metals, &c.-they unite with oxygen, sulphur, and other bodies, without being themselves decomposed, and form with them new compounds, possessed of acid or basic properties.

differing from the true oil of garlic, however, both in composition and in the special character of its smell.

Now, the important points to be borne in mind here,

are

First, That all the compound radicals are capable of combining with sulphur and sulphuretted hydrogen, and of thus forming substances analogous to this mercaptan.

Second, That the number of such organic radicals already known is very great. It is consequently in our power to form many mercaptans, all possessed of very offensive smells, but each distinguished by a shade of offensiveness peculiar to itself. The reader will by this example, therefore, see that in the compounds of sulphur alone the chemist has at his command a very large number of exceedingly foul smells.

4°. Kakodyle.-But arsenic may take the place of sulphur in all these fetid compounds, and produce new volatile substances of which the smell is absolutely insufferable, and which, besides, are deadly poisons. Kakodyle is the name given by chemists to the compound which arsenic forms with the radical methyle. When this volatile substance is exposed to the air it takes fire. As it burns the arsenic contained in it combines with oxygen, and forms white arsenic. This diffuses itself through the air, and when drawn in with the breath acts as a deadly poison.

5°. Alkarsin.-When white arsenic is distilled with acetate of potash, a liquid comes over which has been long known under the name of liquor of Cadet. It is volatile, possesses a peculiar garlic-like fearfully offensive, insupportable, long-enduring smell, and its vapours act as a deadly poison.

This liquor of Cadet is the substance kakodyle, above named, in combination with oxygen. It is known to chemists by the name of Alkarsin.

Because of their abominable smells, and dangerously