Annual Report of the Consulting Chemist. 301 
and in various states of combination, and the nitrogen in guano 
occurs partly in the shape of a number of ammonia salts, and 
partly as uric acid and other nitrogenous organic compounds, 
which are gradually resolved into plant-food on becoming incor- 
porated with the soil. 
The practical effect upon crops of complex manures, such as 
farmyard-manure or Peruvian guano, therefore, is more certain 
and more beneficial upon light soils than that of a simple mixture 
of superphosphate and nitrate of soda. 
As yet none of the new deposits found in the south of Peru 
have been brought into the English market. If in future the 
quality of the new guano deposits should be found to vary to a 
greater extent than has been hitherto the case, it appears to me 
the door would be opened to fraudulent dealings if various kinds 
and qualities of Peruvian guano were put into the manure 
market. 
The proper course for the contractors to pursue, I am inclined 
to think, would be to consign to the factories all cargoes which 
are too damp and lumpy to be applied to the land with advantage 
in a raw state, and to make arrangements in the different ports 
of importation for incorporating high and low quality guano, of 
a good friable character, into one fairly uniform bulk. 
In my'paper " On the Composition of Phosphatic Minerals used 
for Agricultural purposes," I stated that it is not desirable to apply 
any of these minerals, merely in a finely-powdered condition, 
to the land ; and that all phosphatic minerals required to be 
thoroughly decomposed by sulphuric acid, in order to convert 
the insoluble phosphates into perfectly soluble compounds. I 
refer to these statements because parties interested in the sale of 
Redonda phosphate, a mineral composed of phosphate of alumina 
and some phosphate of iron, recommend the use of the phos- 
phate merely in a powdered state, alleging that the application 
to the land of the finely-powdered raw phosphate has given 
satisfaction to agriculturists who have submitted this phosphate 
to the test of field-experiments. The history of artificial manures 
affords abundant evidence of the difficulty of ascertaining by so- 
called practical experiments the real value of manuring agents, 
especially if they are used in the shape of various mixtures ; and 
it is well known that, like figures, field-experiments may be 
employed to prove almost anything that is desired. 
The fact is that Redonda phosphate, like Alto Vela phos- 
phate — another mineral chiefly composed of phosphate of alumina 
— cannot be employed as a raw material in the manufacture of 
superphosphate ; and the extraction of phosphoric acid and the 
manufacture of alum from these minerals as yet has not proved 
to be much of a commercial success. Hence it is very natural 
