162 Mr. W. Sullivan on the Presence of Phosphoric Acid 



accurate results, — in fact the most minute quantities possible 

 may be detected with certainty. The following is the me- 

 thod:— 



When the mineral was limestone, or a substance containing 

 a large quantity of lime, I took about four ounces of it broken 

 into fragments, introduced it into a covered crucible and ex- 

 posed it for three or four hours to a strong white heat; the 

 mass thus treated was then digested in water, when I suspected 

 the substance contained potash or soda, in order to dissolve 

 out these bodies, and strong hydrochloric acid poured on the 

 remainder (if I did not wish to examine for potash, the ig- 

 nited mass was directly treated with the hydrochloric acid); 

 the whole was then evaporated to drj'ness, the dried mass 

 moistened widi a few drops of hydrochloric acid, and then 

 treated with water and filtered to separate undissolved silica ; 

 ammonia was then added to the solution, the precipitate col- 

 lected, well-washed and dissolved in hydrochloric acid; if the 

 mineral contained no iron, or but little of that substance, a 

 few drops of perchloride of iron were added to the solution 

 and then excess of acetate of potash ; if phosphoric acid was 

 present in the most minute quantity, a precipitate, at first light 

 brown, but gradually darkening as it falls to the bottom of the 

 glass, of phosphate iron, was obtained, as this substance is to- 

 tally insoluble in acetate of potash. If the precipitate do not 

 immediately make its appearance, it should be allowed to 

 stand for some time, when it will be perceptible. It some- 

 times happens, when the quantity of the phosphoric acid is 

 extremely minute, that it does not deposit itself for twelve 

 hours; and in one or two instances it ilid not occur until after 

 twenty-four hours. Wh'en the precipitate obtained was large, 

 which was usually the case from the large quantity of the sub- 

 stance employed in the analyses, I invariably verified the re- 

 sult by re-dissolving the precipitate thus obtained and testing 

 with sulphate of magnesia and ammonia and nitrate of silver, 

 which always afforded well-known results where phosphoric 

 acid was present. 



The substances which did not contain lime enough to be 

 treated in the preceding manner were reduced to powder and 

 fused with a mixture of carbonates of potash and soda, or 

 where it was of importance to ascertain the presence of potash, 

 with caustic barytes, and I then proceeded as in the other case. 



It may not be unimportant to mention here, that potash, or 

 rather potash and soda, appear to be as universally present as 

 phosphoric acid : indeed, in none of the minerals which I ex- 

 amined was it totally wanting, though there was frequently but 

 a mere trace. 



