34 Mr. M. Carey Lea on Endotliermic 



will be seen by (3) below that it may amount to as much as 

 over 4 per cent, of the gold present. 



(1) Two or three decigrams of chloraurate with a moderate 

 trituration left 1*8 milligram of metallic gold. Under the 

 action of the pestle the yellow colour of the salt gradually 

 deepened to an olive shade. When water was poured on, the 

 undecomposed salt dissolved, leaving the gold as a delicate 

 purple powder. The colour of the gold being purple instead 

 of the more usual brown shade explains the olive colour just 

 mentioned, yellow and purple combining to form olive. 



(2) Half a gram of the salt was taken. This specimen was 

 more neutral than the preceding, and was therefore more 

 easily reduced. Half an hour's trituration had for effect the 

 reduction of 9*2 milligrams of gold. 



(3) A similar treatment of the same quantity of chloraurate 

 resulted in the separation of 10' 5 milligrams of gold. 



These may seem at first somewhat small proportions. But 

 it is to be recollected that the force is necessarily applied at 

 a disadvantge, and that the equivalent in work of chemical 

 affinity is always very large. In the present case the figures 

 are as follows : — Thomsen found as the heat-equivalent for 

 the combination of gold with chlorine to form auric chloride 

 28*8 great calories. Taking the atomic weight of gold as 

 197, we find that one gram of gold in forming auric chloride 

 disengages 115*7 small calories or water-gram-degrees, whose 

 equivalent, taking Rowland's determination, is 49,288*2 

 gram-metres, corresponding to 4*83 x 10 9 ergs or 483 joules. 



The small quantity of gold reduced in (3), 10*5 milligrams, 

 would by conversion to auric chloride generate 1*215 water- 

 gram-degrees of heat whose equivalent in work is 518 gram- 

 metres. As heat is a degraded form of energy, such an actual 

 transformation without loss to a higher form would be im- 

 possible. It is more correct to say, therefore, that the 

 amount of energy which would raise 518 grams to the height 

 of one metre can be transformed into the same amount of 

 heat, 1*215 water-gram-degrees, as is evolved by 10*5 milli- 

 grams of gold by conversion into auric chloride. Conse- 

 quently this work, 518 gram-metres, represents the amount 

 of mechanical energy transformed into chemical energy in 

 operation (3)*. 



It does not appear that in effecting these reactions and the 



* The amount of energy required would, in fact, slightly exceed this, 

 as the thermochemical equivalent of formation of sodium chloraurate 

 would slightly exceed that of auric chloride. For this chloraurate I do 

 not find a determination, but preferred to use this salt in the operation 

 as being both more stable and more neutral than auric chloride. 



