18 l'HILOSOl'HICAL TRANSACTIONS. [ANNO 1781. 



water. The specific gravity of the strongest concentrated vinegar yet made, is 

 1 .o6g. It is more difficult to find the point of saturation with the vegetable 

 than with the mineral acids ; because they contain a mucilage that prevents their 

 immediate union with alkalis ; and hence they are commonly used in too great 

 quantity. They should be used moderately hot, and sufficient time should be 

 allowed them to unite. 



From these experiments it follows : 1st. That fixed vegetable alkalis take up 

 an equal quantity of the 3 mineral acids, and probably of all pure acids ; for 

 we have seen that 8.3 grains of pure vegetable alkali, that is, free from fixed air, 

 take up 3.55 gr. of each of these acids; and consequently 100 parts of caustic 

 fixed alkali would require 42.4 parts of acid to saturate them. Now Mr. Berg- 

 man has found, that 100 parts of caustic fixed vegetable alkali take up 47 parts 

 of the aerial acid, which, considering his alkali might contain some water, differs 

 but little from my calculation. It should therefore seem, that alkalis have a cer- 

 tain determinate capacity of uniting to acids, that is, to a given weight of acids ; 

 and that this capacity is equally satiated by that given weight of any pure acid 

 indiscriminately. This weight is about 2.35 of the weight of the vegetable 

 alkali. 2dly. That the three mineral acids, and probably all pure acids, take up 

 2.253 times their own weight of pure vegetable alkali, that is, are saturated by 

 that quantity. 



3dly. That the density accruing to compound substances, from the union of 

 their component parts, and exceeding its mathematical ratio, increases from a 

 minimum, when the quantity of one of them is very small in proportion to that 

 of the other ; to a maximum, when their quantities differ less ; but that the at- 

 traction, on the contrary, of that part which is in the smallest quantity to that 

 which is in the greater, is at its maximum when the accrued density is at its 

 minimum, but not reciprocally ; and hence the point of saturation is probably 

 the maximum of density and the minimum of sensible attraction of one of the 

 parts. Hence no decomposition operated by means of a substance that has a 

 greater affinity with one part of a compound than with the other, and than these 

 parts have to each other, can be complete, unless the minimum affinity of this 

 3d substance be greater than the maximum affinity of the parts already united. 

 Hence few decompositions are complete unless a double affinity intervenes ; and 

 hence the last portion of the separated substance adheres so obstinately to that to 

 which it was first united, as all chemists have observed. Thus, though acids 

 have a greater affinity to phlogiston than the earths of the different metals have 

 to it, yet they can never totally dephlogisticate these earths, but only to a cer- 

 tain degree ; so though atmospheric air, and particularly dephlogisticated air, at- 

 tracts phlogiston more strongly than the nitrous acid does ; yet not even dephlo- 

 gisticated air can deprive the nitrous acid totally of its phlogiston, as is evident 



