VOL. LXXII.] PHILOSOPHICAL TRANSACTIONS. 24] 



allow , ■ °-„ for every 15° of heat above or below 55° of Fahrenheit, when the 

 specific gravity of spirit is between 1.400 and 1.500; and -p^Vo when the spe- 

 cific gravity is between 1 .400 and 1 .300. 



A.s to oil and spirit of vitriol, I found the dilatations exceedingly irregular, 

 probably by reason of a white foreign matter, which is more or less suspended or 

 dissolved in it, according to its greater or less dilution. This matter I would not 

 separate, as I intended trying the density of this substance in the state in which 

 it is commonly used. In general I found, that 15° of heat cause a difference of 

 about t-jVo- in its specific gravity when it exceeds 1.800; and of T -^ 5 - 5 . when its 

 specific gravity is between 1.400 and 1.300: its dilatation is greater than that of 

 water, and so much greater as it is stronger. 



The dilatations of spirit of salt are very nearly Deg. Sp. gravity, 



proportional to the degrees of heat, as appears 54 .'!!!"".' u86"o 



by the annexed table. Hence -nrVo should be 66 l 18-20 



added or subtracted for every 21° above or below 128 Kl631 



55°, in order to reduce it to 55°, the degree for which its proportion of acid and 

 water was calculated. The dilatability of this acid is much greater than that of 

 water, and even than that of the nitrous acid of the same density. 



I now proceed to examine the quantity of pure acids taken up at the point of 

 saturation by the various substances they unite with. 



Of the mineral alkali. — That which I made use of was procured from Mr. 

 Turner, who by a peculiar and ingenious process extracts it in the greatest purity 

 from common salt. Of this alkali I rendered a portion tolerably caustic in the 

 usual manner, and evaporating 1 oz. of the caustic solution to perfect dryness, 

 I found it to contain 20.25 gr. of solid matter. I was assured that the watery 

 part alone exhaled during the evaporation, as the quantity of fixed air contained 

 in it was very small, and to dissipate this, a much greater heat would be requisite 

 than that which I used. This dry alkali I immediately dissolved in twice its 

 weight of water, and saturating it with dilute vitriolic acid, found it to contain 

 2.25 gr. of fixed air, that being the weight which the saturated solution wanted 

 of being equal to the joint weights of the water, alkali, and spirit of vitriol em- 

 ployed. 



The quantity of mere vitriolic acid necessary to saturate 100 gr. of pure 

 mineral alkali, I found to be 60 or 6] gr. ; the saturated solution, thus formed, 

 being evaporated to perfect dryness, weighed 36.5 gr. but of this weight, only 

 28.38 were alkali and acid; therefore the remainder, viz. 8.12 gr. were water. 

 Hence lOOgr. of Glauber's salt, perfectly dried, contain 29. 12 of mere vitriolic 

 acid, 48.6 of mere alkali, and 22.28 of water; but Glauber's salt crystallized 

 contains a much larger proportion of water; for 100 gr. of these crystals, being 

 heated red-hot, lost 55 gr. of their weight. This loss I suppose to arise merely 

 vol. xv. I I 



