Ji8 Additional Remarks on the HygromHir end Photometer, 



improper to Call a principle, which in one of Its combinations, is capable of being abforbed 

 by the vertous blood, and of increafing the powers of life, a^ote, I fhall name it, with 

 Dr. Pearfon, Mr. Chaptal, &c. nitrogene, and the gafeous oxide of azote, the properties 

 and compofitiAi of which have been mifunderftood by the chemifts who gave it that name, 

 "nitrous oxide. 



Many months ago I made a number of expcrirtients on the compofition, analyfis, and de- 

 compofition of the ammoniacal falts. ITiefe experiments have afforded me curious and in- 

 . tcrefting refults ; but a wi(h to complcat the invefligation relating to the nitrous oxide have 

 prevented me from purfuing them to their full extent. Among thefe refults, as affording 

 ufeful, pra<Stical applications, I fliall mention the decompofition of the carbonate and ful- 

 phate of ammonia. Carbonate of ammonia undergoes a change in its compofition with 

 every change of its temperature ; on being heated it gives out carbonic acid, and when 

 cooled abforbs it again ; when pafled through « tube, heated red, it is decompounded 

 into water, charcoal^ nitrogene, and hydro-carbonate. Sulphate of ammonia, the partial 

 decompofition of which was difcovered by Mr. Hatchet, when fent through a tube heated 

 red, is decompounded into fulphur, water, and nitrogene. 



I remain, SIR, 



Your's, with much refpefl, 



H. DAVY. 



X. 



Additional Remarks on the Hygrometer and Photometer. By Mr, Jobs Leslie. 



To Mr. NICHOLSON. 

 SIR, 



JLrfOOKING over the notice of the hygrometer and photometer in your Journal, I perceive 

 a few typographical errors, particularly in the punctuation, but which an attentive reader 

 may eafily correct. There is a nriftaJie, however, in the drawing, which it would be 

 proper to redlify : the fliorter branch of the inftrument fliould occupy the centre of the 

 focket, in order that the two balls may ftand in the middle or axis of the cylindrical cafe. 



I forgot to remark that, in frofty weather, when the lower ball is enveloped with a con- 

 gealed cruft, the fame degrees of drynefs in the air will be marked by fomewhat larger fpaces 

 on the fcale of the hygrometer. For in that cafe evaporation has a double office to per- 

 form, converting the film of ice fucceffively into the liquid and into the aeriform ftate; the 

 former procefs expends 75° centigrade of heat, and the latter 524°, and hence the fize of the 

 correfponding divifions are to be conceived augmented in the proportion of 75xS24> to 524» 

 or tha,t of 8 to 7 ; that is, to obtain the real drynefs in time of froft, one-eighth part muft be 

 4 deduced 



