1825'.! Dr, Thomson* s First Principles of Chemistry, 143 



gases or vapours exist composed of one volume of carbon 

 vapour and one volume of hydrogen gas. He says, *' the first 

 consists of 



1 volume carbon vapour? ^^^^^^^^^^^ j^t^ i ^^i^^^. 

 1 volume hydrogen gas 3 



"Its specific gravity is 0*4861. One volume of it requires 

 for complete combustion l-i volume of oxygen gas. After the 

 combustion there remains one volume of carbonic acid gas. 



" This pecuhar gas has not yet been met with by chemists ; 

 but I see no reason to doubt its existence." 



Now, in the name of the first principles of chemistry as esta- 

 blished by experiment, we protest against the admission of so 

 vague a conjecture in a work decidedly of a practical kind ; and 

 it is venturing much too far to state the specific gravity of a gas 

 which exists only in the imagination ; and equally objectionable 

 is it to state the quantity of oxygen which it does require for 

 combustion, instead of that which it ivould require if we could 

 "Jirst catch it." Under this head Dr. Thomson states his 

 analysis ofnapthaUne, by which it appears to consist of ■" ■■ 



1-i- atom carbon. . , . .^ v«w ♦ . • '. . . .... 1*125 § VHr*'^' 



] atom hydrogen . .>i\'i w ^i. * k * 0'125^'fiJi^f »'* 



In determining the atomic weights of siHcon, an experiment 

 is related, which we confess ourselves at a loss to comprehend : 

 it is the following : ^ 



" About the middle of May, 1823, 1 fused a quantity of silica, 

 with thrice its weight of anhydrous carbonate of soda, and 

 digested the fused mass in a small quantity of water, till the silica 

 assumed a flocky appearance. The whole was then thrown 

 upon a filter ; and the sifica was washed repeatedly with distilled 

 water, till no traces of soda could be found in the washings. 

 In two days the filter with the silica became dry enough to be 

 handled. I placed the filter on several folds of blotting paper, 

 on a table in the middle of my laboratory, where it was allowed 

 to remain for six weeks, without being disturbed. It may be 

 necessary to mention, that the weather during the whole time 

 was uncommonly cold ; and I have reason to believe, that the 

 temperature of the room scarcely ever exceeded 60°, if it 

 amounted to so much. When I returned to Glasgow, on the 

 24th of June, the thermometer in my laboratory stood at 57°. 

 The sihca, to the eye and the feel, appeared perfectly dry ; it 

 weighed 43*23 grains. By exposure to a red heat, it lost lO-S^. 

 grains, and was reduced to 3268. Now, 32 68 : 10-55 :: 4 : 

 1-2913 == water combined with 4 silica. This exceeds 1-125 by 

 0-1663, which is rather more than one-seventh of an atom. This 

 may be con^ifei^d the greatest amount of the excess whichever 

 remains;" "-^^'^'^ « .. 



