VOL. LXXIV.] PHILOSOPHICAL TRANSACTIONS. 483 



I never heard of any fixed air being produced by the burning of sulphur or 

 phosphorus ; but it has been asserted, and commonly believed, that lime-water is 

 rendered cloudy by a mixture of common and nitrous air ; which, if true, would 

 be a convincing proof that on mixing those 2 substances some fixed air is either 

 generated or separated; I therefore examined this carefully. Now as common air 

 usually contains a little fixed air, which is no essential part of it, but is easily 

 separated by lime-water ; and as nitrous air may also contain fixed air, either if 

 the metal from which it is procured be rusty, or if the water of the vessel in which 

 it is caught contain calcareous earth, suspended by fixed air, as most waters do, 

 it is proper first to free both airs from it by previously washing them with lime- 

 water.* Now I found, by repeated experiments, that if the lime-water was clean, 

 and the two airs were previously washed with that substance, not the least cloud 

 was produced, either immediately on mixing them, or on suffering them to stand 

 upwards of an hour, though it appeared by the thick clouds which were produced 

 in the lime-water, by breathing through it after the experiment was finished, that 

 it was more than sufficient to saturate the acid formed by the decomposition of 

 the nitrous air, and consequently that if any fixed air had been produced, it must 

 have become visible. Once indeed I found a small cloud to be formed on 

 the surface, after the mixture had stood a few minutes. In this experiment the 

 lime-water was not quite clean ; but whether the cloud was owing to this cir- 

 cumstance, or to the air's having not been properly washed, I cannot pretend 

 to say. 



Neither does any fixed air seem to be produced by the explosion of the inflam- 

 mable air obtained from metals, with either common or dephlogisticated air. 

 This I tried by putting a little lime-water into a glass globe fitted with a brass cock, 

 so as to make it air tight, and an apparatus for firing air by electricity. This 

 globe was exhausted by an air-pump, and the two airs, which had been pre- 

 viously washed with lime-water, let in, and suffered to remain some time, to 

 show whether they would affect the lime-water, and then fired by electricity. 

 The event was, that not the least cloud was produced in the lime-water, when 

 the inflammable air was mixed with common air, and only a very slight one, or 

 rather diminution of transparency, when it was combined with dephlogisticated 

 air. This however seemed not to be produced by fixed air; as it appeared in- 

 stantly after the explosion, and did not increase on standing, and was spread 



* Though fixed air is absorbed in considerable quantity by water, as I showed in Phil. Trans, 

 vol. 56, yet it is not easy to deprive common air of all the fixed air contained in it by means of water. 

 On shaking a mixture of 10 parts of common air, and 1 of fixed air, with more than an equal bulk of 

 distilled water, not more than half of the fixed air was absorbed, and on transferring the air into fresh 

 distilled water only J the remainder was absorbed, as appeared by the diminution which it still suffered 

 on adding lime-water. — Orig. 



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