24 BULLETIN OF THE BUSSEY INSTITUTION. 
ble with its contents is placed in a larger Hessian crucible, a cover is put 
upon the latter, and the whole is placed in the anthracite fire of a stove 
or furnace, such as are used for warming houses in this part of the 
country. In this way, the platinum crucible may be exposed to very 
intense radiant heat without the least risk of any foreign matter getting 
into it or of its being injured either by the fire or by the earthen cruci- 
bles. Care must bé taken, of course, that the crucibles are not heated 
too quickly, lest the pasty mass of rock and carbonate should boil over 
through the sudden evolution of carbonic acid. 
Fusion having been accomplished, the mass was treated with dilute 
nitric acid. It was found in every instance that the rock had been com- 
pletely decomposed. The nitric acid solution was evaporated upon a water 
bath, and the residue was heated upon the bath (but at no higher tem- 
perature) for a long time, in order to render the silica insoluble, the heat- 
ing being persisted in until no trace of acid fumes could be detected. 
Jn many instances, the silica had to be heated several days upon the 
water bath, in order to free it completely from the adhering acid. The 
thoroughly dried silica, etc., was moistened with nitric acid, the mass was 
treated with water, the silica * was collected upon a filter and thoroughly 
washed, the filtrate and wash waters were evaporated to the volume of 
about 100 cc., a solution of molybdate of ammonia, prepared according 
to Fresenius, was added to it, and the acid mixture was kept at a tem- 
perature of about 75° during six or eight hours, or until the phosphoric 
acid had been completely precipitated. The yellow precipitate was dis- 
solved in warm dilute ammonia, and filtered in the usual way, the filtrate 
was nearly neutralized with chlorhydric acid, and a very small excess of 
magnesia mixture as recommended by Fresenius+ was added, together 
with as much strong ammonia as was equal to one-third the volume of 
the liquid, which did not exceed 100 or 110 cc. all told. The mixture, 
after standing over night, was filtered, and the precipitate was collected, 
washed, ignited, and weighed with the precautions enjoined by Fresenius. 
Lime was determined in the usual way ; viz., by fusing the powdered 
rock with an excess of carbonate of soda, treating the fused mass with 
* In order to test the question, how much, if any, phosphoric acid was re- 
tained by these bulky silica precipitates, an experiment was made as follows: 
The thoroughly washed, still moist silica, equal to about 27 ce. in bulk, that 
had resulted from the decomposition of rather more than ten grammes of a 
syenite rich in quartz, was percolated, little by little, with 100 cc. of strong 
ammonia water, then washed with water, and the percolate and washings were 
evaporated to dryness at 100°, with the addition of a small quantity of nitric 
acid. The residue was moistened with nitric acid, was treated with hot water 
and filtered. The filtrate, on being digested with molybdate of ammonia at 80° 
during six or seven hours, gave a very slight yellow precipitate, which, when dis- 
solved in ammonia and treated with magnesia mixture, gave a mere trace of 
precipitate, altogether too small to admit of estimation. 
+ “ Anleitung zur Quantitaven chem. Analyse,” 1873, p. 403. 
