66 SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS, [bull.itc. 
salts are first boiled together in neutral solution for a few minutes and 
to the cooled solution ammonia is added. The results are said to be 
remarkably exact. 
METHODS OF COLLECTING AND IGNITING THE PRECIPITATE. 
If the blast has not to be employed, the weight of the pyrophosphate 
can doubtless be most accurately arrived at by collecting and igniting 
the precipitate in a Gooch crucible, provided the asbestos felt is well 
constructed and not of the serpentine variety so largely on the market. 
Neubauer ignites slowly in platinum after drying, without removing 
from the paper, applying the blast only when the carbon has been 
wholly burned off. 1 
Almost as exact are the two modifications of the method in use for 
phosphate analyses at the agricultural experiment stations at Danzig 
and Lisbon, described by Schmoeger 2 and Mastbaum. 3 According to 
the former the precipitate after drying is detached from the paper and 
placed in a platinum crucible, followed by the folded filter. To the 
covered crucible the full flame of a burner is applied, and after a short 
time the burning off of the carbon is accomplished with the crucible 
open. A short blasting follows. In a number of experiments on quan- 
tities ranging from 0.06 to 0.28 gram of pyrophosphate the results 
were, with a few exceptions, naturally lower than those obtained on 
duplicates by the ordinary method of igniting, but only by 0.0013 
gram in maximum. 
Mastbaum, to shorten time, applies the full flame to the moist pre- 
cipitate wrapped in its filter. Later, when most of the carbon is 
burned off, he moistens the residue with two or three drops of strong 
nitric acid, evaporates this carefully, heats with full burner for a few 
minutes, then blasts for half a minute. He describes the results as 
irreproachable. In this laboratory only the Mastbaum modification 
has been tried, and it certainly seems to be satisfactory when the ex- 
treme of accuracy is not required. 
At one time the procedure first recommended by Ulbricht, later by 
Broockmann, and also by L. L. de Koninck, was used. It consists in 
dissolving the ammonium-magnesium phosphate off the filter with 
nitric acid, collecting the filtrate in a weighed crucible, evaporating 
the contents to dryness, 4 and subsequently igniting, the product being 
presumably pyrophosphate. But it was soon observed that the ignited 
salt, especially when large in amount, does not always dissolve com- 
1 Zeitschr. fur anal. Chemie, Vol. XXXIII, p. 362, 1894. 
2 Ibid., Vol. XXXVII, p. 308, 1898. 
3 Ibid.,p.581,1898. 
4 A pink color of varying intensity almost invariably becomes apparent as the mass approaches dry- 
ness, a most delicate test for the traces of manganese which always escape precipitation by ammo- 
nium sulphide or bromine. 
