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The several kinds of air I ufually keep in cylindrical jars, as c, c, fig. 1, about ten inches. long, and 2 wide, being fuch as I have generally used for electrical batteries, but I have likewife veffels of very different forms and fizes, adapted to particular experiments.

When I want to remove veffels of air from the large trough, I place them in pots or dishes, of various sizes, to hold more or lefs water, according to the time that I have occafion to keep the air, as fig. 2. These I plunge in water, and flide the jars into them; after which they may be taken out together, and be fet wherever it shall be most convenient. For the purpose of merely removing a jar of air from one place to another, where it is not to ftand longer than a few days, I make use of common tea-dishes, which will hold water enough for that time, unless the air be in a ftate of diminution, by means of any procefs that is going on in it.

If I want to try whether an animal will live in any kind of air, I first put the air into a finall veffel, just large enough to give it room to stretch itself; and as I generally make use of mice for this purpose, I have found it very convenient to use the hollow part of a tall beerglafs, d fig. 1, which contains between two and

three

three ounce measures of air. In this veffel a mouse will live twenty minutes, or half an hour.

water.

For the purpose of these experiments it is most convenient to catch the mice in small wire traps, out of which it is eafy to take them, and holding them by the back of the neck, to pass them through the water into the veffel which contains the air. If I expect that the mouse will live a confiderable time, I take care to put into the veffel fomething on which it may conveniently fit, out of the reach of the If the air be good, the moufe will foon be perfectly at its eafe, having fuffered nothing by its paffing through the water. If the air be fuppofed to be noxious, it will be proper (if the operator be defirous of preferving the mice for farther ufe) to keep hold of their tails, that they may be withdrawn as foon as they begin to fhew figns of uneafinefs; but if the air be thoroughly noxious, and the mouse happens to get a full infpiration, it will be impoffible to do this before it be abfolutely irrecoverable.

In order to keep the mice, I put them into receivers open at the top and bottom, standing upon plates of tin perforated with many holes, and covered with other plates of the fame kind, held down by fufficient weights, as fig. 3.

...These

receivers

receivers ftand upon a frame of wood, that the fresh air may have an opportunity of getting to the bottoms of them, and circulating through them. In the infide I put a quantity of paper or tow, which must be changed, and the veffel wafhed and dried, every two or three days. This is moft conveniently done by having another receiver, ready cleaned and prepared, into which the mice may be transferred till the other fhall be cleaned.

Mice must be kept in a pretty exact temperature, for either much heat or much cold kills them prefently. The place in which I have generally kept them is a fhelf over the kitchen fire-place where, as it is ufual in Yorkshire, the fire never goes out; fo that the heat varies very little, and I find it to be, at a medium, about 70 degrees of Fahrenheit's thermometer. When they had been made to pass through the water, as they neceffarily must be in order to a change of air, they require, and will bear a very confiderable degree of heat, to warm and dry

them.

I found, to my great furprize, in the course of thefe experiments, that mice will live intirely without water; for though I have kept them for three or four months, and have offered them water feveral times, they would never tafte it ;'

and

and yet they continued in perfect health and vigour. Two or three of them will live very peaceably together in the fame veffel; though I had one inftance of a moufe tearing another almoft in pieces, and when there was plenty of provifions for both of them.

In the fame manner in which a mouse is put into a veffel of any kind of air, a plant; or any thing else, may be put into it, viz. by paffing it through the water; and if the plant be of a kind that will grow in water only, there will be no occafion to fet it in a pot of earth, which will otherwise be neceffary.

There, may appear, at first fight, fome difficulty in opening the mouth of a phial, containing any fubftance, folid or liquid, to which water muft not be admitted, in a jar of any kind of air, which is an operation that I have sometimes had recourfe to; but this I eafily effect by means of a cork cut tapering, and a strong wire thrust through it, as in fig. 4, for in this form it will fufficiently fit the mouth of any phial, and by holding the phial in one hand, and the wire in the other, and plunging both my hands into the trough of water, I can easily convey the phial through the water into the jar; which must either be held by an affiftant, or be fastened by strings, with its mouth projecting

over the fhelf. When the phial is thus conveyed into the jar, the cork may easily be removed, and may also be put into it again at pleasure, and conveyed the fame way out again.

When any thing, as a gallipot, &c. is to be fupported at a confiderable height within a jar, it is convenient to have fuch wire ftands as are represented fig. 5. They anfwer better than any other, because they take up but little room, and may be easily bended to any fhape or height.

If I have occafion to pour air from a veffel with a wide mouth into another with a very narrow one, I am obliged to make ufe of a funnel, fig. 6, but by this means the operation is exceedingly eafy firft filling the veffel into which the air is to be conveyed with water, and holding the mouth of it, together with the funnel, both under water with one hand, while the other is employed in pouring the air; which, afcending through the funnel up into the veffel, makes the water descend, and takes its place. These funnels are beft made of glafs, becaufe. the air being visible through them, the quantity of it may be more easily estimated by the eye. It will be convenient to have feveral of these funnels of different fizes.

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