1822.] Dr. Apjohn on the Specific Gravity of Gases. 385 



silver, where it remained for 14 hours without being affected. 

 Part of this was made the connecting wire between the north 

 and south poles of two bar magnets, when it became speedily 

 plumed with crystals of silver." 



Now I do assert that if Mr. Murray believed in the accuracy 

 of his own experiments, he was totally ignorant of the action of 

 steel upon nitrate of silver ; for in this experiment he has stated, 

 and attempted to prove, that no action takes place. The expe- 

 riment is indeed fallacious, but then it proves even more than Mr. 

 Murray's ignorance of the facts with which he asserts that he 

 was acquainted. 



I had intended to offer a few more observations upon some 

 parts of Mr. Murray's reply which I understand, and quoted 

 others that I do not comprehend ; but, I think, I have done 

 enough. In parting with him, I would advise him in future, 

 should his experiments excite any further notice, not to employ, 

 in his reply, such terms as " rude " and '* ungentlemanly ; " 

 they are harmless, except to the reputation of him who uses them. 

 I am. Sir, your obedient servant, 



B. M. 



Article XII, 



Remarks on the Influence of Moisture in modifying the Specific 

 ^ Gravity of Gases. By James Apjohn, MD. 



(To the Editor of the Annals of Philosophy.) 



SIR, Trinity College^ Dublin^ J pril 20, 1822. 



Upon reading (in the number of the Annals for this month), 

 Dr. Thomson's Observations on the Specific Gravities of the 

 Gases as modified by Moisture, it at first struck me that some 

 mistake had been committed in attributing to steam at 212° only 

 the specific gravity of -472. Into this opinion I had been led 

 by recollecting that Dr. Ure, in his Dictionary of Chemistry, had 

 stated it so high as •625. A closer examination, however, 

 proved that the specific gravity given it by Dr. Ure was too 

 great, and indicated, as the probable source of the error, the 

 assumption of air at 21 2° as the unit of comparison. Dr. Thom- 

 son has not overlooked this circumstance in his paper, but his 

 mode of estimating the effect of moisture on the densities of the 

 gases appears to me altogether incorrect. The principle of the 

 method adopted by Dr. Lre for the same purpose is true, but his 

 number for steam being too high, his results are erroneous. As 

 this is a subject of some importance, I trust I shall be excused 

 for entering a little into detail. It has been shown by Dalton 

 New Series, vol. in. 2 c 



