1 825.] Dr, Thomson's Answet* ta Mri "timnf, ^3 



. Mr. Ralny's paper is written with all that perspicuity, accu- 

 racy, and modesty, which I looked for from him ; and had he 

 taken into his consideration all the circumstances of the cas0^^ ^ 

 his conclusions would have been undoubted. But I flatte? 

 myself that I shall be able to satisfy him that if I have commit^ 

 ted any error in my calculations, it lies exactly on the opposite 

 sijde: from what he supposes ; and that instead of underrating, 

 I flayein reahty overrated the weight of the moisture which the 

 hydrogen gas ought to have contamed, on the supposition that 

 th(& theory of vapour at present adopted is correct. '^^^ » '' *' ^ 



In niy recent work, to which Mr. Rainy allude^,' l^^ld'^itiBt 

 consider it proper to enter into any details. I have not even 

 noticed all the data which were employed by me in calculating 

 the quantity of vapour in the hydrogen gas. It will be requisite, 

 therefore, to state some particulars of the experiments a little in 

 detail that the grounds of the calculations may be fully und^r^' 



,Thftweigbit.:€*f lihe small flask in which I dissoiW^a^^i^ iinb) 



w^$:7B6'9 grains. Its capacity was 8*8 cubic inches. *''^^^ ^ftoitrr 



y'jrhe dilute sulphuric acid employed for drssoil^i»^ th^lfe^fii^' 



a mixture of very nearly ■ t oi ^mwjummm lOi b^ltri 



Water 1700 grs. 



Sulphuric acid. . . , , 400 



sd thai tM'ttsuar weight of the gla^s filled with dilute 'Sulphuric 

 acid was ^886*9 grains. This weight was not rigidly the sanie 

 in different experiments ; because the acid and water were 

 measured and not weighed. But the difference scarcely; 

 exceeded eight grains, except in aJew cases when the quantities 

 were purposely varied. 



/jthe boiling point of my dilute acid was always 224°, except 

 in two or three trials in which the acid was made stronger on 

 purpose ; but as none of these trials were employed in my deter- 

 mination of the specifiChg|-^MityiiPf. hydrogen gae^^'^li'nreed not 

 bring them under review.;^** ^.j^iillfn' uUi!/;lo > 



The length of the glass tube filled with chloride of calcium 

 was 15 inches, and it^ weight when so filled varied from 815 

 grains to 820 grains in different experiments. K.uiH'U; v^ >'i *< s-^i^^i 



j^hont two cubic inches of the flask were Mt^'enip'tyi^^^^tW^ 

 zinc was introduced while the flask was kept in a sloping po^f^^'* 

 tion, and this position was maintained during the whole tini^"^ 

 that the zinc was dissolving. This was to prevent any small 

 drops that might be elevated by the escape of the hydrogen gas 

 from making their way out of the flask. It was kept undei* 



* The\« ig a typographical error m vol. i. p. 67, line 9 from bottom, of my late jvoik^^J 

 Instead c^,'^ about 18 cubic inches," it should have been ** about 8 cubic inches,^^ VL / 



New Series, vol. x. 2 a y^nt^m 



