Analyses of the Ashes of Plants. 
171 
0\iilo Grain's in 
of Iron. 1000 of li(iiiiil. 
1st CXI). 87 • 5 measures gave 2 • 83 = 3-230 
•2ntl „ 48-5 1-56 = 3--216 
3i'd „ 28-5 ,, 1-55 = 3-207 
It will be seen that a slight difference exists in the results ob- 
tained by the two operators, but that the numbers in each series 
are almost identical. It is unnecessary to say that this is due to 
trifling variation in the method of reading off the quantities, and 
in no way affects the accuracy of analyses so performed. In 
proof of the accuracy of the estimation of phosphoric acid by the 
addition of iron, we must refer to the different experiments quoted 
before, more especially to the series of white peas and white 
mustard-seed, which were analysed in this Avay. It is incon- 
ceivable that these results should be sO nearly alike, were there 
anything radically defective in the process of estimating the phos- 
phoric acid. We have latterly, however, found it more convenient 
to adopt another system for the estimation of phosphoric acid, 
which is as follows : — 
The solution of the ash in hydrochloric acid is treated as usual 
with acetate of ammonia, for the separation of the oxide of iron 
as phosphate. The lime is next thrown down by neutral oxalate 
of ammonia (acetic acid being the only free acid present) ; the 
liquid is then divided into two portions — to one ammonia is added 
(and, if necessary, phosphate of soda), to precipitate magnesia ; 
and to the other portion sulphate of magnesia and ammonia are 
added, and the phosphoric acid estimated as phosphate of 
magnesia. 
That this method gives accurate results as respects the lime, 
phosphoric acid, and magnesia, will, we think, be evident from 
the following experiment : — 
The solution in hydrochloric acid of 10 grains of the ash of 
white peas was treated with acetate of ammonia, and after the 
separation of the phosphate of iron a solution of iron was added 
to precipitate the phosphoric acid ; the phosphate of iron so ob- 
tained was converted, by Fresenius's process, into ])hosphate of 
magnesia, which weighed 5-98 grains, equal to 37 '89 per cent, of 
phosphoric acid in the ash. From the solution to which the iron 
liquid had been added, the lime was precipitated by oxalate of 
ammonia and ammonia, yielding 2- 18 of carbonate of lime, equal 
to 6- 10 per cent, of lime. The magnesia was then precipitated 
by phosphate of soda, giving 1 • 95 of pyrophosphate, equal to 
7 * 14 per cent, of magnesia. 
Twenty grains of the same ash dissolved in hydrochloric acid, 
and the iron separated by acetate of ammonia ; oxalate of am- 
jnunia added to separate the lime, giving 4-40 of carbonate of 
