VOL. LXXI.] PHILOSOPHICAL TRANSACTIONS. 9 



spirit of salt, whose specific gravity is I.O98, that is, 3.55 gr.; the remainder of 

 11 gr. is therefore mere water, viz. 7-45 gr.; consequently, if the density of the 

 acid and water had not been increased by their union, the specific gravity of the 

 pure and mere nitrous acid should be 1 1.8729; for the specific gravity of this 

 acid should be as its absolute weight divided by its loss of weight in water, and 

 this loss should be as the total loss of these 1 1 gr. minus the loss of the aqueous 



part. Now the total loss = — — = 7-749, and the loss of the aqueous part 

 = 7.45, consequently the loss of the acid part is 7-749 — 7-45 = O.299, and 

 therefore the specific gravity of the acid part, that is, of the pure nitrous acid, 



j s _3. _ j 1,8720. But it is well known, that the density of the nitrous acid, 



0.296 - J 



as well as that of the vitriolic, is increased by its union with water; and there- 

 fore the loss above found is not the whole of its real loss in its natural state (if 

 it could be so found) but partly the loss that arises from the density that accrues 

 to it from its union with water; for since its density is increased by this union, 

 its loss is less than it would be if the nitrous acid had only its own proper den- 

 sity, and consequently the specific gravity above found is greater than its real 

 specific gravity. 



To determine therefore the real specific gravity of this acid in its natural state, 

 the quantity of accrued density must be found, and subtracted from the specific 

 gravity of the spirit of nitre, whose true mathematical specific gravity will then 

 appear. I endeavoured to effect this by mixing different portions of spirit of nitre 

 and water, remarking the diminution of their joint volume below the sum of 

 the spaces occupied by their separate volumes; but could never attain a sufficient 

 degree of precision. The following method, though not exactly accurate, I 

 found more satisfactory ; 1 2 gr. of the spirit of nitre, whose specific gravity by 

 observation was 1.389, contained, as I supposed from the former experiment, 

 3.55 gr. of acid, and 8.45 of water; then if the specific gravity of the pure 

 nitrous acid were 11.872, the specific gravity of this compound of acid and 

 water should be 1.371; for the loss of 3.55 gr. acid should be O.299, and the 



12 



loss of the water 8.45; the sum of the losses 8.749; — — - = 1.371 ; but, asal- 

 ready said, the specific gravity by observation was 1.389, therefore the accrued 

 density in this case was at least .018, the difference between 1.38g and 1.37 1. I 

 say at least, for as the specific gravity 11.872 was certainly too high, the loss 

 of 3.55 gr. acid was certainly too small; and if it were greater, the mathema- 

 tical specific gravity 1.371 would have been still lower. However, .018 is cer- 

 tainly a near approximation to the degree of density that accrues to 3.55 gr. acid 

 by their union with 7.45 gr. of .water, and differs inconsiderably from the truth, 

 as will appear by the sequel; therefore, subtracting this quantity from 1.419, we 

 have nearly the mathematical specific gravity of that proportion of acid and water, 



VOL. XV. C 



