620 
On the Analysis of Soils. 
100 grains of the said aril, dried at 212', abwjrb 8 grains of moisture 
in 24 hours ; while 100 grains of the comparatiTely cteril scil of 
Regent's Park, dried equally, absorb only 5 grains : a difference due 
chiefly to the finer comminution of the former. 
Since the phosphates are such precious ingredients towards fertilizing 
soils, it is desirable to possess a clear and simple test of their presence. 
For this purpose digest the soil, for an hour or so, with a moderate heat, 
in dilute nitric axnd, freeftom muriatic (tiz. which affords, when largely 
diluted, no precipitate, by the addition of a solution of nitrate of sflver). 
Throw the mixture on a filter, and to the filtered liquid add potash-water, 
cautiously, till the instant that a precipitate begins to appear ; then drop 
into it a weak solution of nitrate of silver. If any pho^horic salts be 
prteenr, a yellowbh precipitate will immediately fall, which is re-soluble 
in a 1 excess of nitric acid. Whatever is not thus dissolved is chloride 
of silver, and ought to be separated by filtration : on adding then weak 
water of potash (not ammonia) cautiously to the filtered liquid, the pure 
phosphate of silver will be obtained^ without any alumina or iron, pro- 
vided the liquid be still acidulous in a slight degree. It ought to be 
remembered that chloride of silver falls in a white curdy form, quite 
different from that of the phosphate of silver. Tlie portion of soil used 
for this experiment should be fresh, and not calcined, because the phos- 
phates, when ignited, afford white precipitates with salts of silver. The 
stronger the solution of the phosphoric saline compound is, the more 
characteristic is the yellow precipitate with silver ; and then ammonia may 
be used for effecting the partial saturation of the acid excess. Sulphate 
of magnesia is an excellent re-agent for detecting phosphoric acid, and 
for separating it from the above acid solution, when it is partially nra- 
tralized with ammonia; for the magnesia forms, with the phosphoric 
acid and ammonia, the insoluble granular precipitate of ammonia-mag- 
nesian phosphate. A solution of sulphate of magnesia, containing a 
little sal-ammoniac, is pn>bably the b^ test-liquor for detecting phos- 
phates in faintly acidulous, but still better in neutral, solutions. 
In almost all soils of an arable nature under cultivation in this 
country, there is a sufficiency of calcareous matter present to counteraxrt 
the combination of phosphoric acid with alumina or oxide of iron, for 
which reason it would be an idle refinement of agricultural analysis to 
search for phosphates of alumina and iron. As for manganese, often 
a^sr^ciated with iron, it exists in to ) small a proportion, and is possessed 
of too little value to make it WL>rth while to effect its separation. It 
gives to calcined iron-oxide a black hue, and is characterized in its saline 
solutions by the flesh-coloured precipitate which it affords with hydro- 
sulphuret of ammonia, after the whole of the iron has been thrown down 
by boiling the solution of the two metals with pure carbonate of lime. 
The organic matter in any soil may be correctly estimated by cal- 
cining its powder pretty strontly till ;he carbonic acid be expelled from 
the lime in it. The loss of weight, deducting that due to the carbonic 
acid gas (which is known from an independent experiment), gives the 
quantity of organic matter. Its quahty is determmed by the ultimate 
analysis by means of hydrate of soda and quicklime, as previously 
staled. 
