ell long, and that for this reason that the attached bladder may not be destroyed during the operation by the heat of the furnace or by the hot vapours.) Into this bladder I pour some milk of lime (§ 22), and press the air out as fully as possible. This lime will absorb the aerial acid during the distillation, and leave the phlogisticated acid of nitre untouched. (c.) In exactly the same way as is described in a I also collect aerial acid and the inflammable air of sulphur (of which I shall speak further on). But if the bladders are moist, or even if only the air surrounding them is so, both these kinds of air penetrate completely through the bladders in a few days; if the bladders and air are dry, however, this does not take place. I obtain inflammable air from the metals, as iron or zinc, in exactly the same way, except that I place the bottle in warm sand. This air is still more subtle than the preceding; it penetrates through the fine pores of the bladder in a few days, although air and bladder are dry.

I frequently experienced this to my vexation. (d.) I not infrequently catch air in bladders, without any bottles. I place in a soft bladder (AA, Fig. 4) the material from which I intend to collect the air, for example, chalk; above this chalk I draw the bladder together with twine BB; I then pour above it the acid diluted with water and press out the air as completely as possible; I finally tie up the bladder above at CC. I then untie the twine B, when the acid runs upon the chalk; it immediately drives out the aerial acid, whereupon the bladder must expand. (e.) When I require to get an air out of the bladder into a flask, glass, retort, or bottle, I fill such apparatus with water and place in it a tightly fitting cork; I then tie the bladder which contains the air, that is, the opening from C to D (Fig. 4), very firmly over such bottle; I then invert the bottle so that the bladder comes below and the bottle above, whereupon I hold the bottle with the left hand and with the right I withdraw the cork; I hold this cork firmly between both fingers inside the bladder until the water has flowed out of the bottle into the bladder, and the air has mounted out of the bladder into the bottle; I then put in the cork and detach the bladder from the bottle. When I wish to preserve the air for a long time I place the neck of the bottle in a vessel with water. (f.) When there is aerial acid in the bladder, or another air which can unite with water, and I wish to unite it with water neatly, I fill a bottle with cold water, and, after it has been attached to the bladder, I permit about the fourth part to run into the bladder; I then push the cork, which, as previously, was firmly held within the bladder, into the bottle again; I then shake the bottle gently, when the air will dissolve in the water. Thereupon I make a small opening by means of the cork, when air passes out of the bladder into the bottle in order to fill up again the space which has become empty,

without any water running into the bladder; I then push the cork again into the bottle and shake the water contained in it. I repeat this operation two or three times more, when the water is saturated with this air. (g.) When I wish to mix together two kinds of air in a flask or bottle, I permit in the first place just as much water, by measure, to run from the bottle filled with water, into the bladder, as I wish to have of air. I then tie the bottle over with a bladder filled with another kind of air and permit the remaining water to run into the bladder, whereupon I immediately replace the cork in the bottle, as soon as the last of the water has run out. (h.) When I wish to have in a bladder an air collected in a bottle, I reverse the operation. That is to say, I fill the bladder with as much water as I wish to have in it of air and tie it up at the top; I then tie this bladder tightly over the top of the bottle and untie the ligature of the bladder, draw the cork out of the bottle and so permit the water to run out of the bladder into the bottle. I then tie up the bladder, which now contains the air out of the bottle, and detach it from the bottle. (i.) When I have in a bottle an air mixed with another kind of air which can be absorbed by water or lime, but wish to know how much of each kind is present in the bottle, I tie over it a bladder into which so much milk of lime has been poured that the bottle can be filled with it; I then withdraw the cork and permit the water or milk of lime to run into the bottle. I afterwards invert the bottle and permit the milk of lime to flow again into the bladder; I repeat this running out and in several times. So much air by measure has been absorbed as there now remains behind of milk of lime in the bottle.

These are the methods which I employed in my investigations of air. I admit that they will not particularly please some, because they do not decide

with great exactness. They afforded me satisfaction, however, in all my investigations; and people will often split a hair where it is not in the least necessary.

31. Continuation of the Experiment mentioned in § 29 ...

Anyone might object and say that the air obtained according to § 29 is perhaps nothing else than a dry acid of nitre converted into elastic vapours. But if this opinion had any foundation, this air should not only be corrosive, but should also produce nitre anew with alkalies. This, however, does not occur. Nevertheless, this objection would possess considerable weight were I not able to prove that several substances produce the same air as the acid of nitre does during distillation. But proof of this is not wanting.

I have proved in a treatise on manganese, which is to be found in the Transactions of the Royal Swedish Academy of Sciences for the year 1774, that this mineral is not soluble in any acid unless an inflammable substance be added, which communicates the phlogiston to the manganese, and by this means effects an entrance of the latter into the acids. I have shown in the same place that vitriolic acid, nevertheless, during a strong distillation with powdered manganese, unites with it and makes it soluble in water; and if this manganese is separated again from the vitriolic acid by means of precipitating agents, there are found in it the most distinct traces of the inflammable substance.... I had already observed a few years ago, that if in the calcination of manganese with oil of vitriol in an open crucible, some coal dust was driven by the current of air over the surface of this mixture, these fine coals took fire in the same instant with very great brilliancy. I accordingly made the following experiments.

32. First Experiment.—I mixed so much con

centrated oil of vitriol with finely powdered manganese that it became a stiff magma. I distilled this mixture from a small retort on the open fire. In place of a receiver I made use of a bladder, empty of air, and, in order that the vapours which might pass over should not attack the bladder, I poured into it some milk of lime (§ 30, letter b). As soon as the bottom of the retort became red hot, an air passed over which gradually expanded the bladder. This air had all the properties of a pure fire-air.

33. Second Experiment.—When I distilled two parts of finely pulverised manganese with one part of the phosphorous acid of urine in the same way as is indicated in the preceding paragraph, I likewise obtained fire-air.

34. Third Experiment.—(a.) I dissolved in aqua