V26 



Prognostics of 

 change in the 

 barometer. 



EXPERIMENTS ON SULPHURIC AC*D. 



Again, in the morning the hygrometer is generally higher 

 than at noon, by reifon of the difference of temperature ; but 

 if it ftands lower at noon in a greater proportion than the dif- 

 ference of temperature demands, it prognoliicates fair wea- 

 ther. — On the contrary, if at noon it be higher than it flood in 

 the morning, rain may be expected. SaufT. Hygr. p. 356. 



To forefee the Rife or Fall of the Barometer in Day-time. 



Obferve it at feven o'clock in the morning, and afterwards 

 at nine and at ten. If it remains fteady, its next motion will 

 probably be downwards. So alfo if it falls within that interval 

 of time, the probability is, that it will fink Hill lower. But if 

 it rifes within that interval, the chances of a greater rife or of 

 a greater fall are equal. 



Again, obferve the barometer at one in the afternoon, and 

 again at three ; if it remains unmoved, it is probable that it 

 will rife, but if it has fallen, the chances of a farther rife or 

 fall are equal. 



XI. 



Uncertainty in 

 the analyfis of 

 pyrites from the 

 combuftion of 

 the fulphur. 



The burned ful. 

 phur, or fulph. 

 acid, precip. by 

 b-irytes. 



Ohfervations and Experiments undertaken with a View to deter- 

 mine the Quantity of Sulphur contained in Sulphuric Acid ; and 

 of this latter contained in Sulphates in general. By Richard 

 Chenevix, F. R. S. and M. R. I. A. (Irifti Acad. 1802.) 



IN a paper which I had the honour to prefent to the Royal 

 Society of London, and the fubject of which was the analyfis 

 of fome arfeniates of copper, and of iron, I had occafion, in 

 examining many pyrites, matrices of thofe ores, to remark the 

 very great inequality which prevailed in the refults of repeated 

 experiments, made with a view to determine the proportion 

 of fulphur. But I foon perceived, that the inaccuracy was 

 caufed by a partial combuftion and acidification of the radical, 

 through the means of the nitric acid, employed to diflblve the 

 ore. 



Having therefore, in the ufual manner, ascertained what 

 quantity of that ingredient remained untouched, I was forced 

 to feek the reft of it in the liquor, which had waflied the va- 

 rious precipitates. To obtain it, I poured a folution of nitrate 



of 



