183 



On the Specific Gravity of the Gases, [MARCHj^ 



18. The specific gravity of carbonic oxide in the table was 

 found by Mr. Gruickshank, the original discoverer of this gas. 

 I do not know that his experiment has ever been repeated with 

 requisite care. I have myself more than once taken the specific 

 gravity of this gas ; but as the specimens which 1 tried were 

 never perfectly free from carbureted hydrogen, I do not consider 

 imy resuhs so accurate as those of Cruickshank. 



19. The specific gravity of hydrophosphoric gas was deter- 

 mined by Sir Humphry I)avy when he discovered it, and the 

 result of his experiments published in the Philosophical Trans- 

 actions, part 2d. We shall give an account of them in our 

 present number. 



20. The specific gravity of steam was determined by Trales, 

 1 do not know the method which he employed, nor how far the 

 accuracy of his result may be depended on. 



21. The specific gravity of ammonia given in the table is that 

 found by Sir Humphry Davy. As it is the latest, and as he 

 was acquainted with all that had been done by Bertholiet and 

 Henry, and as he was at' considerable pains, I consider it as 

 likely that his result approaches most nearly to accuracy. Biot 

 and Arrago found the specific gravity of ammonia 0°59669, 

 which coincides very nearly with the number in the table. 



22. The specific gravity of carbureted hydrogen as given in 

 the table was determined by myself. The experiments may be 

 found in the first volume of the Memoirs of the Wernerian 

 Society of Edinburgh. Sir Humphry Davy makes it a little 

 lighter. He found it 0-491 , Gruickshank made it 0'67774. 

 Dalton 0-600. My experiments are nearly the rneaa between 

 all these, and therefore are probably nearest the truth. 



23. The specific gravity of arsenical hydrogen gas was ascer- 

 tained by Trommsdorf. 



24. The specific gravity of phosphureted hydrogen gas is not 

 yet determined in a satisfactory manner. I have given two 

 different results. The first was found by Mr. Dalton and Dr. 

 Henry ; the second by Sir Humphry Davy. 



25. The specific gravity of hydrogen gas has been very often 

 determined. Sir Humphry Davy makes it 0*074, The number 

 in the table I consider as, approaching as nearly to accuracy as 

 possible, in the present state of our knowledge. It is the result 

 of many trials, at low temperatures; and the quantity of vapour 

 present was calculated according to Dalton's tables, and allowed 

 for. 



Upon the whole, I. flatter myself that this table, such as it is^ 

 will be of considerable service to practical chemists. 



