868 JDr. Thomson's A^iswtr to Mr, Rami/. [Nov., 



gen gas carries along with it and deposits in the chloride of 

 calcium small quantities of sulphuric acid, or of sulphate of zinc, 

 or of both together.* 



Whether Mr. Rainy will consider an experiment which comes 

 within less tlian one per cent, of the ratio of 1 to 16, as esta- 

 bhshing the truth of that ratio, I cannot pretend to conjecture. 

 But 1 am sure that I am not able to come nearer the truth by 

 means of the balance which 1 employed. I am not at, all certain 

 that the real weight of the hydrogen was not 0*02 grain less 

 than 1 reckon it ; for notwithstanding the goodness of the beam, 

 and the scrupulous attention with which every thing was weighed, 

 it is scarcely possible to guarantee a deviation from accuracy to 

 .so small an amount as 0*02 grain when the whole weight amounts 

 to 4769-91 grains, or not much short of a troy pound. This was 

 weighing to -^__i__-th part of the whole, a degree of precision to 

 which I believe it to be very difficult to attain. 



But it was not by means of these experiments that I satisfied 

 myself of the truth of the ratio between the specific gravities of 

 hydrogen and oxygen gases. The evidence already brought 

 forward was conclusive. My object was merely to produce an 

 approximation by means so simple as would be hkely to satisfy 

 those who had not the requisite knowledge to draw their conclu- 

 sions from more complicated sources. It may be worth while to 

 mention a few of the facts upon which my opinion was originally 

 founded. 



1. I determined by actual experiment that the specific gravity 

 of hydrogen gas is 0*0694. The subsequent determination of 

 Berzelius and Dulong will be found to approach so near to this, 

 that I have often been surprised that these ingenious gentlemen 

 did not perceive that 0*0694 approaches more nearly to the mean 

 of their experiments than the number which they themselves 

 pitched upon. 



2. I consider the evidence which I have adduced in my late 

 work as conclusive that air is a mixture or compound of one 

 volume of oxygen gas and four volumes of azotic gas, or of one 

 atom oxygen and two atoms azote. From this it follows that 

 the specific gravity of oxygen gas must be 1*1111, if atmospheric 

 air be reckoned unity. 



3. The specific gravity of ammoniacal gas, deduced from a 

 mean of the determinations of Sir H. Davy and my own, is 

 0*590237. It has been proved I consider to the satisfaction of 

 every person that it is a compound of one volume of azotic 



, • The diloridc of calcium would not merely imbibe the moisture contained in the 

 inr^rogen gas passing through it ; but it would be constantly absorbing the atmosphere 

 "^vapour m the enmtv w.irt of tbi- smiill fl:isk. Now as the experiment always lasted 



*^^htuh4 iiim not : more vapour mi^ht bo a]?^fl(i;t>^ than 



tnrough the chloride. 



-f"|ij^jt)fpfig^ble^<i. ^, .1. I.!: ^ciiiture in, the hydrogen; gas v/hich passed 



the chic 



