104 Mr. Shelf ord Bidwell [May 5, 



inert dust — in virtue of which it acquires an abnormal power of 

 promoting aqueous condensation. 



I thought that possibly some clue as to the nature of this property 

 might be obtained by observing how some other gases and vapours 

 behaved ; but though the experiments I made perhaps tend to 

 narrow the dimensions of the mystery, I cannot say that they have 

 completely solved it. Indeed some of the results only introduce 

 additional perplexities. 



One of the most natural things to try is hydrochloric acid, which 

 is known to have a strong affinity for water. If we heat a little of 

 the acid solution in a test-tube, closed with a cork, through which a 

 glass tube is passed, and direct the issuing stream of gas upon the 

 jet, the densest condensation results. [Experiment.] The vapours 

 of sulphuric and nitric acids also cause dense condensation, and I sup- 

 pose both of these have an affinity for water. But so also, and in an 

 equally powerful degree, does the vapour of acetic acid ; yet the 

 affinity of this acid for water, as indicated by the heat evolved when 

 the two are mixed, is very small. 



Ammonia gas, when dissolved in water, causes the evolution of 

 much heat. Yet a stream of this gas directed upon the jet has no 

 action. [Experiment.] 



Ozonised air, which Mascart found so effective in his experiments 

 with the closed vessel, is quite inoperative with the steam jet. 

 Equally so is the vapour of boiling formic acid, which I believe is 

 chemically a much more active acid than acetic, and has a lower 

 electrical resistance. (See Table.) 



Condensation of Steam Jet. 



Active. 



Air, oxygen or nitrogen, in which electrical discharge is occurring. 

 Burning and incandescent substances. 

 Fumes from phosphorus. 

 Hydrochloric acid. 

 Sulphuric acid vapour. 

 Nitric acid vapour. 

 Acetic acid vapour. 



Inactive. 



Air, &c, in which electrical discharge has ceased for about 10 seconds. 

 Smoke without fire. 

 Bottled phosphorus fumes. 

 Ammonia. 

 Ozone. 

 Steam. 



Alcohol vapour. 

 Formic acid vapour. 

 Sulphurous acid. 



It seems that we have here a pretty little problem which might, 

 perhaps, be solved without much difficulty by a competent chemist, 



