VOL. LXXI.J PHILOSOPHICAL TRANSACTIONS. 7 



substances in alloy is found, may not be generally known, I shall here mention 

 them in the words of Mr. Cotes. 



" The data requisite are the specific gravities of the mixture and of the two 

 ingredients. . . . Then, as the difference of the specific gravities of the mixture 

 and the lighter ingredient is to the difference of the specific gravities of the mix- 

 ture and the heavier ingredient, so is the magnitude of the heavier to the mag- 

 nitude of the lighter ingredient. Then, as the magnitude of the heavier multi- 

 plied into its specific gravity, is to the magnitude of the lighter multiplied into 

 its specific gravity, so is the weight of the heavier to the weight of the lighter. 

 Then, as the sum of these weights is to the given weight of either ingredient, 

 so is the weight given, to the weight of the ingredient sought." Thus, in this 

 case, I.O98— 1.000= .098 is the magnitude of the heavier ingredient, viz- 

 the marine acid ; and .098 X 3.100 = 0.3038 the weight of the marine acid ; 

 and, on the other hand, 3.100 — I.O98 = 2.002 the magnitude of the water, 

 also 2.002 X 1.000 = 2.002 its weight ; the sum of these weights is 2.3058 : 

 then, if 2.3058 parts of spirit of salt contain 0.3038 parts acid, 17 gr. of this 

 spirit of salt will contain 3.55 acid. In the same manner it will be found, that 

 23.35 gr. of spirit of salt, whose specific gravity was 1.115, contained 3.55 gr. 

 acid. 



The point of saturation was pretty accurately found by putting the glass 

 cylinder which contained the alkaline solution on the scale of a very sensible 

 balance, and at the same time weighing the acid liquor in another pair of scales, 

 when the loss of weight indicated the escape of nearly equal quantities of the 

 fixed air contained in the solution ; then the acid was gradually added, by dipping 

 a glass rod into it, to the top of which a small drop of acid adhered : with this 

 the solution was stirred, and very small drops taken up and laid on bits of paper 

 stained blue with radish juice. As soon as the paper was in the least reddened, 

 the operation was completed, so that there was always a very small excess of 

 acid, for which half a grain was constantly allowed ; but no allowance was made 

 for the fixed air, which always remains in the solution ; but as, on this account, 

 only a small quantity of the alkaline solution was used, this proportion of fixed 

 air must have been inconsiderable. If an ounce of the solution had been em- 

 ployed, this inappreciable portion of fixed air would be sufficient to cause a sen- 

 sible error : for I judged of the quantity of fixed air lost by the difference be- 

 tween the weight added to the 100 gr. and the actual weight of the compound. 

 When this difference amounted to 2.2 gr. I then judged the whole of the fixed 

 air expelled, and found it to be so, as 100 gr. of this alkaline solution, being 

 evaporated to dryness in a heat of 300°, left a residuum which amounted to lO-i- 

 gr. ; which 104 gr. contained 2.2 gr. of fixed air, as will hereafter be seen. 



Hence 8.3 gr. of pure vegetable fixed alkali, free from fixed air and water, or 



