18 MEMOIR ON EMERY. 



a mortar of convenient size and the extremity of a feather or 

 a small brush it is possible to lose but an insensible quantity 

 of the mineral, and to estimate with sufficient precision the 

 amount of silica abraded from the mortar. 



Another method by which I accomplished the levigation in 

 some of the analyses was in a steel mortar of the same form as 

 the agate mortar; and when completed the powder was placed 

 in a glass with nitric acid diluted with thirty times its weight 

 of water, and left in it for one hour, agitating it occasionally. 

 The iron taken from the mortar was dissolved, and no part of 

 the mineral attached. The next thing was to filter, and con- 

 tinue the analysis with the substance thus freed from the iron 

 of the mortar, without any second weighing. 



Of these two methods I preferred to employ the first for the 

 emery, as it is more expeditious and almost if not quite as 

 exact as the second. There are, however, occasions in which 

 the steel mortar should be resorted to. 



The substance once reduced to an impalpable powder, it was 

 necessary to render it completely soluble, and my researches to 

 arrive at this were long and tedious. In trying the various 

 known methods the most successful was found to be that with 

 a mixture of carbonate of soda and caustic soda heated to 

 whiteness for one hour; nevertheless I could not obtain a com- 

 plete decomposition. The decomposition might probably be 

 completed if the levigation was made more thoroughly; but it 

 is easy to understand that with a large number of analyses of 

 the same substance to make, it was a desideratum on my part 

 not to consume the best part of a day in the levigation of a 

 single gramme, particularly as I did not wish to confide this 

 operation to another, as much care was required to lose noth- 

 ing during the levigation. Mixed with carbonate of baryta 

 and heated in a forge, the decomposition of the mineral was 

 far from being complete; the same may be said for the treat- 

 ment with the caustic alkalies in a silver crucible. 



The bisulphate of potash decomposes it almost entirely by 

 a single operation, but unfortunately a double salt of potash 

 and alumina is formed which is almost insoluble in water or in 

 the acids, and it is only by a solution of potash that it is first 

 decomposed and afterward redissolved. I will not stop to 

 detail all the disadvantages attending this method, but will at 



