

the Hejjian Pyrites. 367 



eluded air, which cannot be difcharged; as is 

 often the cafe with caft fulphur, and alfo the retires. 



XV. At laft, all the bodies muft be weighed, m 

 the mod accurate manner, on an aiTay-balance of 

 equal weight, one grain thereof anfwering exactly 

 to fix lines : all bodies, weighing three drachms, 

 have, for the above obfervations, been weighed 

 with the utmoft accuracy. 



XVI. But for examining the comparative gra- 

 vity of falts, as alum, borax, vitriol, fal-gem, 

 &c. inftead of water, rectified fpirit of wine is to 

 be ufed, as not diflblving therein in the courfe of 

 the weighing. 



XVII. In order to weigh a coftly body, of which 

 a heavy piece cannot be had, or if too heavy^ none 

 of it can be ftruck off, look in the table for a body- 

 approaching tolerably near to it in fpecific gravity, 

 and of this laft weigh, on the afTay- balance, an 

 equal weight againft the coftly body; then weigh 

 both in water ; laftly, add to or fubftract their dif- 

 ference from the known body in the table, accord- 

 ing as the coftly body happens to be lighter or 

 heavier, and you procure the true fpecific gra- 

 vity of the coftly body, by the proportion in the 

 table. 



A curious and ufeful contrivance for ordering a tall cy- 

 lindrical glafs in fuch a manner \ that upon pouring 

 into it an unknown [aline water ', the hydroftatical 

 balance Jhall inftantaneoujly^ without a calculus, 

 Jhew the number of grains or drachms of fait in a 

 found of the f aline water. 



f \.) Caufe to be made a tall cylindrical glafs, 

 about twelve inches high, and two and a half thick; 



(2.) fill 



