i'9 
ficant. In some cases merely a pinch. It is insignificant in a 
sense and is readily replaced by incidental increments hitherto 
much; but not wholly disregarded. In Johnson’s Agriculture 
Chemistry, p. 3, the author says: — 
il It is extremely difficult nay impossible, to estimate exactly 
u what quantity of plant food is present in a soil in a condi- 
tion available for the plant’s immediate needs. This is 
“ really best ascertained by experimenting with the plant 
“itself.” Professor Johnson also states it to be one of the 
objects of the farmer to test the opinions of theoretical men, 
‘'for it is only on a basis of often repeated, skilfully con- 
" ducted, and faithfully recorded experiments, made by in- 
“ structed persons, that true theories can ever be successfully 
“ built up, hence (we say) the importance of experiments in 
“practical Agriculture 
What the incidental or natural increment of plant food on an 
acre of land in Trinidad is we do not know, but it is quite evident 
that it exists, and has to be counted on by the Agriculturist in 
cropping his land. A large amount of incidental plant food is 
evidently conveyed by rain water. How much we don’t know as 
no regular analysis of our rain waters is available. It appears 
probable also that the fertility given by the deposited excreta of 
small animals, birds, insects, and worms and reptiles and the decay 
of their bodies, upon the ground, and also the decay of vegetable 
matter, dust deposited by wind, leaves, flowers, seeds and branches, 
&c., is largely in excess of what has been previously estimated, 
and in fact is, of as much importance as food obtained from the 
reserves held by the soil itself. This must be known as the “ inci- 
dental increment” and must be taken into full account in all Agri- 
tural operations . — Agricultural Bulletin, Trinidad, April igoi. 
PHOSPHATES AND PHOSPHORIC ACID. 
As superphosphates and other phosphatic manures are coming 
pretty largely into use, it is desirable that the exact meaning of the 
above terms should be well understood. For though all phosphates 
contain phosphoric acid, yet in quotations from an analysis given 
by a manufacturer or seller it is all important to have a definite 
statement of which of the two substances is meant. For the value 
of the manure depends on the available phosphoric acid it contains. 
On this subject Mr. Pearson, Government Agricultural Chemist 
of Victoria, thus advises the farmers : — 
“ It has been reported to me that farmers in some of the country 
districts who are intending to order manure for the coming season 
are likely to be somewhat misled as to the relative meaning of 
phosphoric acid and phosphates. Some years ago it was the cus- 
tom to value phosphatic manures according to the amount of phos- 
phate of lime contained in them. But as there are no less than 
four different kinds of phosphate of lime, each of which contains 
different proportions of phosphoric acid and lime, confusion and 
misunderstanding arose from this method of representing the value 
