Phosphntic Materials^ used for A(/ricnlfnral Pi/rposrs. 373 
analysis is almost always contaminated with oxalate of magnesia, 
and tluuel'ore make it a g-eneral practice to redissolve the par- 
tially-washed precipitated phosphate of magnesia in ammonia, 
and to throw it down a second time. The magnesia precipitate 
must be washed with strong ammonia water. 
The lime precipitate generally continues a variable and often 
altogether insignificant proportion of phosphate of iron and 
alumina. In ordinary analyses, it is hardly necessary to take 
any notice of the traces of phosphate of iron, which exist in good 
white samples of bone-ash. For very minute analyses, I dissolve 
the lime precipitate, after having been weighed, in hydrochloric 
acid, precipitate the solution with ammonia, collect precipitate 
on a small filter, wash and redissolve on filter, and precipitate a 
second time in the cold. The phosphate of iron and alumina, 
after washing, is free from lime. Its weight is determined, and 
deducted from the first weight of the lime precipitate. In order 
to obtain the phosphoric acid contained in the phosphate of iron 
and alumina, the precipitate is dissolved in hydrochloric acid, a 
little tartaric acid is added, then ammonia, and finally the phos- 
phoric acid is determined as phosphate of magnesia. If necessary, 
a separate determination of carbonic acid and sulphuric acid is 
made in the bone-ash. 
As regards accuracy, this plan of analysis leaves nothing to 
be desired. A proof of this is furnished in the subjoined analyses 
of the same sample of bone-ash ; two of them were made by 
myself, and two by my first assistant, Mr. Sibson. 
Though all ordinary care is taken in preparing a sample for 
analysis, it is next to impossible to obtain a perfectly homogeneous 
powder. The trifling discrepancies in the results of the four 
separate analyses are due, perhaps, in a higher degree to this 
circumstance than to the method of analysis. 
Composition of a Sample of Bone-ash. 
1st Analysis. 
2nd Analysis. 
3rd Analysis. 
4th Analysis. 
6 
34 
6 
34 
6 
35 
6 
35 
Organic matter (chiefly charcoal) 
38 
2 
83 
3 
26 
2 
84 
34 
95 
34 
48 
34 
89 
34 
83 
44 
35 
43 
93 
43 
59 
43 
99 
1 
12 
1 
19 
71 
97 
Insoluble siliceous matter (sand) 
8 
43 
9 
34 
9 
39 
8 
83 
Carbonic acid and alkalies (de-) 
1 
1 
89 
1 
81 
43 
2 
19 
100 
00 
100 
00 
100 
00 
100 
00 
* The phosphoric is equal to tri-l 
basic phosphate of lime (bone-> 
75 
72 
74 
71 
75 
59 
75 
4G 
earth) ) 
Average percentage of bone-earth 
"5 
32 
