416 M. O. Lea — Endothermic Decompositions hy Pressure. 



and the gold appears in the metallic state so that it can be 

 weighed and the exact amount of reduction can be fixed. It 

 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 color of the salt gradually deep- 

 ened to an olive shade. When water was poured on, the unde- 

 com posed salt dissolved, leaving the gold as a delicate purple 

 powder. The color of the gold being purple instead of the 

 more usual brown shade explains the olive color just men- 

 tioned, 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 reduc- 

 tion of 9*2 mgs. of gold. 



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

 resulted in the separation of 10*5 mgs. of gold. 



These may seem at first somewhat small proportions. But 

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

 disadvantage and that the equivalent in work of chemical affin- 

 ity is always very large. In the present case the figures are as 

 follows : Thomsen found as the heat equivalent for the com- 

 bination 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-meters corre- 

 sponding to 4*83 X 10 9 ergs or 483 joules. 



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

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

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

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

 transformation without loss to a higher form would be impos- 

 sible. It is more correct to say, therefore, that the amount of 

 energy which would raise 518 grams to the height of one 

 meter can be transformed into the same amount of heat, 1*215 

 water-gram-degrees, as is evolved by 10 5 mgs. of gold by con- 

 version into auric chloride. Consequently this work, 518 gram- 

 meters represents the amount of mechanical energy transformed 

 into chemical energy in operation [3].* 



It does not appear that in effecting these reactions and the 

 others which remain to be described, mechanical energy under- 



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

 thermochemical equivalent of formation of sodium chloraurate would slightly ex- 

 ceed that of auric chloride For the 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. 



