446 
On Phosphatic Guanos. 
5. Several of the samples contained a considerable amount of 
sulphuric acid, which appears to have been mainly combined 
with lime. 
6. ^lejillones guano also contains magnesia, amounting on 
an average to about 3 per cent. 
7. Chloride of sodium (common salt) to the extent of about 
2^ per cent, was also found in the several samples. 
8. The percentage of insoluble siliceous matter (sand) varied 
from 1 to 4 per cent., in round numbers, in the six samples. 
9. All contained but very little oxide of iron. Of alumina, 
only traces could be detected. Practically speaking, Mejillones 
guano may be regarded as free from oxide of iron and alumina. 
On combining the proportions of carbonic and sulphuric acid 
with lime, and the magnesia with phosphoric acid to form tri- 
basic phosphate of magnesia, it will be found that the remainder 
of the phosphoric acid in the preceding analyses is more than 
sufficient to form tribasic phosphate with the rest of the lime. 
It appears from these results that JNIejillones guano contains, in 
addition to the ordinary bone-phosphate, a combination of lime 
with phosphoric acid, which is less basic than the tricalcic phos- 
phate. Such a compound is bibasic phosphate of lime. The 
occurrence of this phosphate in JNIejillones guano is of some 
practical importance, for it is well known that bibasic phos- 
phate of lime is more readily dissolved by water, or perhaps, 
more correctly speaking, yields soluble phosphoric acid to water 
more easily than the ordinary tribasic phosphate. Or if we 
combine the lime with carbonic, sulphuric, and phosphoric acid 
to form carbonate and sulphate of lime, and tribasic phosphate 
of lime, an excess of phosphoric acid will remain, which, 
according to this mode of calculation, is united with mag- 
nesia to form monobasic or bibasic phosphate of magnesia, or a 
mixture of the two. These magnesian phosphates are still more 
soluble in water than the corresponding lime phosphates, and 
hence, whether we adopt one or the other modes of combining 
the basic with the acid constituents, the practical result remains 
the same in either case. ^Mejillones guano certainly is a more 
readily soluble and efficacious phosphatic manure than similar 
fertilisers which do not contain more phosphoric acid than is 
necessary *o form tribasic phosphate with lime. 
The greater readiness with which Mejillones guano yields 
phosphoric acid to plants, in comparison with other phosphatic 
guanos, its richness in phosphates, and the extremely fine state of 
subdivision of its particles, unquestionably characterise !Mejil- 
lones guano as one of the most valuable phosphatic guanos at 
present imported into England. 
In addition to the preceding more complete analyses, the 
