_The loss of gold in cupellation_ is by no means always inconsiderable. In three cupellations of 1 gram of gold with 20 grams of lead made purposely at a very high temperature the cupel absorbed 6.04, 6.20, and 6.45 milligrams of gold. Hence at a high temperature there may easily be a loss of more than half a per cent. of the gold. In ten cupellations with the same quantities of gold and lead, but at an ordinary temperature, the gold recovered from the cupels varied from 1.37 to 1.92 milligrams, and gave an average of 1.59 milligrams. In round numbers the cupellation loss of pure gold is .15 per cent. But if the gold be alloyed with _silver_ the loss is diminished, as is shown by the following experiments. Gold, .3 gram, was cupelled with 10 grams of lead and varying amounts of silver, and the cupels were assayed for gold with the following results: Silver in the alloy .3 gram .6 gram .9 gram Gold in the cupel .47 milligram .32 milligram .17 milligram These, calculated on the .3 gram of gold, give the loss as .157, .107 and .057 per cent. respectively. The effect of _copper_, on the other hand, is to increase the cupellation loss, which, silver being absent, may from this cause rise to .3 per cent., even when the temperature is not excessive. In the ordinary assay of gold-copper alloys a constant weight of the alloy is always taken; hence as the weight of copper in a cupel charge increases, the weight of gold decreases. The silver, on the other hand, is always very nearly two and a half times as much as the gold, whatever its quantity may be. But the cupellation loss is smaller with less gold and greater with more copper, and it so happens in these assays that these two opposites nearly neutralise one another. Mr. W.F. Lowe[26] found the gold recoverable from the cupels on which 20 grains of gold bullion had been treated varied only between .014 and .015 grain (_i.e._ from .07 to .075 per cent. of the bullion treated), although the quality of the bullion varied from 9 to 22 carat.[27] But in the poorest bullion there was only 7.5 grains of pure gold, while in the richest there were 18.3 grains; yet each lost on the cupel the same weight of gold, viz., .014 grain. When reckoned in percentages of the actual gold present the losses are .187 per cent. and .076 per cent. respectively. The heavier percentage loss is mainly due to the increased quantity of copper. As with silver so with gold the predominant cause of the cupellation loss is the solution of the metal in the molten litharge which passes into the cupel. Three lots of 1 gram of gold cupelled each with 20 grams of lead repeatedly, so as to make 13 cupellations in all, lost in actual weight 35.72 milligrams. The gold recovered from the cupels amounted altogether to 34.56 milligrams. This shows that, compared with the absorption by the cupel, the other causes of loss are inconsiderable.