HISTOBY OF THE ATOMIC THEORY. 1 49 



" If X is greater than y there appears still no obstacle to 

 prevent complete precipitation. 



" But if X is less than y, so that only a part of B can be 

 displaced, a portion of the dissolved precipitant must be 

 sensibly thrown down, so as to act anew, or some other 

 assistance must be given. 



«' II. Let n 7 I et m Z. nm 



** With respect to phlogiston, this is the same result as in 

 case I., but the obstacles are less." 



(That is, if the acid for dissolving the precipitating metal 

 is less than the acid which dissolves the metal to be precipi- 

 tated, as in this case, the precipitating metal would not cease 

 its action for want of acid.) 



"III.) Let n z. 1 then is m 7 nm. In this case B cannot 

 be entirely thrown down, unless nx =^ y or nx 7 y, because 

 only n 100 of the precipitant A is dissolved." 



(That is, if it requires more acid to dissolve the precipi- 

 tating metal than the one in solution, then the metal in 

 solution cannot be quite thrown down, unless it should be 

 found that the amount of phlogiston in the precipitant is 

 equal to the amount in the precipitate, or greater than it.) 



Then, after recounting experiments, the first of which are 

 made with a nitric acid solution, he says, p. 139 ; 



" Therefore 135 parts of mercury have reduced completely 

 into the metallic form by means of their phlogiston, 100 parts 

 of silver which had been dissolved and calcined. This had 

 united with four times its weight of mercury, and crystallized 

 in an arborescent form. 



" The amount of lead necessary for precipitating 100 lbs. of 

 dissolved silver, amounts to 234 lbs. *♦»*♦*• 



" C. 375 lbs. of shining plates of copper were put into a 

 solution of silver, and were soon covered with a crystalline silver 

 coating. When all the silver had fallen, the copper plates, 

 when well cleaned, were found to have lost 31 lbs. The pre- 

 cipitated silver was found to amount to a cwt. (100 lbs.) 



