8 PHILOSOPHICAL TRANSACTIONS. [ANNO 1781 . 



10.5 of mild fixed alkali, were saturated by 3.55 gr. of pure marine acid, and 

 consequently the resulting neutral salt should, if it contained no water, weigh 

 J 1.85 gr. ; but the salts resulting from this union (the solution being evaporated 

 to perfect dryness in a heat of l6o° kept up for 4 hours) weighed at a medium 

 1 2.66 gr. Of this weight, 11.85 gr. were acid and alkali ; therefore the remainder, 

 viz. 0.81 gr. were water; therefore 100 gr. of perfectly dry digestive salt contain 

 28 gr. acid, 6.55 water, and 65.4 of fixed alkali. 



I was then curious to compare my experiments with those made by others, 

 but could not find any made with sufficient precision except those of Mr. Hom- 

 berg in the Paris Memoirs for 1699. However, as to spirit of salt I did not 

 think proper to compare them, as he mentions that his could dissolve gold, and 

 therefore was probably impure. 



Of spirit of nitre. — The common reddish brown or greenish spirit of nitre 

 containing, besides acid and water, a certain portion ot phlogiston; and being 

 also mixed with some portion of the acid of sea salt, I judged it unfit for these 

 trials; and therefore used only the dephlogisticated sort, which is quite colour- 

 less, and resembles pure water in its appearance. This pure acid cannot be made 

 to exist in the form of air, as Dr. Priestley has shown; for when it is deprived 

 of water and phlogiston, and furnished with a due proportion of elementary fire, 

 it ceases to have the properties of an acid, and becomes dephlogisticated air: I 

 could not therefore determine its proportion in spirit of nitre, as I had done that 

 of the marine acid, but was obliged to use another method. 1st. To 1 963 .25 

 gr. of this spirit of nitre, whose specific gravity was 1.419, I gradually added 

 1795 gr. of distilled water: and when it cooled I found the specific gravity of 

 this mixture I.389. 2dly. To 1984.5 gr. of this I again added 178.75 gr. of 

 water; its specific gravity was then 1.362. 



I then took 100 gr. of a solution of fixed vegetable alkali, whose specific gra- 

 vity was 1 .097, the same as I had before used in the trials with spirit of salt, and 

 found this quantity of alkali to be saturated by 1 1 gr. of the spirit of nitre, 

 whose specific gravity was 1.41 9; and by 12 gr. of the spirit, whose specific 

 gravity was 1.389; an d ty 13.08 of that whose specific gravity was 1.30'2. The 

 quantities here mentioned were the mediums of 5 experiments. I found it neces- 

 sary to dilute the nitrous acid with a small proportion of water, of which 1 kept 

 an account. When I neglected this precaution, I found that part of the acid 

 was phlogisticated, and went off with the fixed air. Note also, that after each 

 affusion of acid, 10 minutes were allowed for the matters to unite; a precaution 

 which I also found absolutely necessary. 



Hence, on the supposition that a given quantity of fixed vegetable alkali is sa- 

 turated by the same weight of both acids, we see that 1 1 gr. of spirit of nitre, 

 whose specific gravity is 1.41 9, contain the same quantity of acid as 27 gr. of 



