296 
OXALIC ACID IN PERUVIAN GUANO, 
evaporation, abundant crystals of neutral oxalate of ammonia, 
the mother-water containing a certain quantity of phos[)hate 
and sulphate of ammonia. 
If guano is moistened with cold water and left alone for 
some time, the results are very different. The pro[)ortion of 
oxalic acid contained in the solution goes on diminishing, 
and the filtered liquid contains phosphoric instead of oxalic 
acid. After remaining in contact for twenty-four hours, the 
quantity of phosphoric acid becomes so considerable that the 
filtered liquid, boiled with sulphate of magnesia, yields, with¬ 
out the addition of ammonia, an abundant crystalline pre¬ 
cipitate of phosphate of magnesia and ammonio-magnesian 
phosphate. 
It is easy to explain why phosphoric acid, under these 
circumstances, should become soluble; in fact, it is evident 
that the oxalate of ammonia, dissolved by the addition of 
water to the guano, is gradually transformed in presence of 
phosphate of lime, and that the result of the reciprocal action 
of these two salts is insoluble oxalate of lime and soluble 
phosphate of ammonia. 
It will be seen from this that the phosphoric acid of guano 
is not dissolved, because the manure contains at the same 
time oxalic acid ; for by distributing all the fixed bases of 
the guano between phosphoric acid, sulphuric acid, and 
chlorine, there remain for the phosphoric acid only two 
equivalents of lime and magnesia, forming with it a salt 
partially soluble in neutral salts of ammonia. The presence 
of oxalic in the aqueous solution of guano is a sufficient 
reason for the absence of lime. 
The following fact seems to contradict the explanation 
given above :—Recently-precipitated phosphate of lime, with 
two or three equivalents of base, is scarcely at all modified 
by long contact ^Yith oxalate of ammonia ; traces only of 
phosphoric acid are found in solution. But it must be ob¬ 
served that guano always contains a body which facilitates 
decomposition, sulphate of ammonia. This salt renders the 
phosphate of lime partly soluble, but it does not pass into 
the solution in this form, the lime being immediately pre¬ 
cipitated by the oxalic acid, the action of the sulphate of 
ammonia being prolonged, and the decomposition of the 
phosphate of lime goes on. By adding a small quantity of 
sulphate of ammonia or a few^ drops of hydrochlorate of the 
same base to a mixture of oxalate of ammonia and phosphate 
of lime, the phosphate is very rapidly changed into oxalate. 
In guano moistened with water the transformation of 
oxalate of ammonia to the state of phosphate goes on rapidly 
