53 
plant foods. Where are we to buy our nitrogen, phosphoric acid, 
and potash? If you were to go to a manure dealer and say you 
wanted a ton of nitrogen, he would probably stare at you; he 
would not know what you meant. In the Melbourne market the 
principal source of nitrogen as a plant food is sulphate of 
ammonia, which is obtainable at the gas company’s office for 
£12 10s. ton. Ammonia exists in coal gas as it first comes 
from the retorts, and must be removed before the gas is fit for 
consumption. It is removed by passing the gas through sul- 
phuric acid, which absorbs and combines with the ammonia, 
forming the crystalline salt known as sulphate of ammonia. 
Ammonia consists of nitrogen to the extent of over 82 per cent., 
and sulphate of ammonia contains 21 per cent. of nitrogen. Now, 
from these figures we can ascertain the money value of nitrogen. 
If sulphate of ammonia, containing 21 per cent. of nitrogen, sells 
at £12 10s. per ton, then the nitrogen must be worth close on 
£60 per ton. But the simplest method of reckoning its value is 
to consider what would be the price of a material containing only 
1 per cent. of nitrogen. Thus, sulphate of ammonia containing, as 
it does, 21 per cent. of nitrogen is sold at £12 10s. per ton, there- 
fore a substance containing only 1 per cent. would be worth close 
-on 12s. per ton. Thus we calculate the money values of manures 
according to the value of 1 per cent. of the essential ingredients 
per ton. So if we have presented to us a substance containing 
84 per cent. of readily soluble nitrogen, we know that it must be 
worth eight and a half times 12s., that is to say, £5 per ton. 
Another source of nitrogen is nitrate of soda. This contains 
only 16 per cent. of nitrogen, and its value, according to 
what we have already seen, would be sixteen times 12s., 
that is to say, £9 12s. per ton. But, as a matter of fact, it 
is never sold in Melbourne for less than £18, that is to say, 
nearly twice its value.* In Europe, with its cold winters, the 
nitrogen in nitrate of soda is more quickly taken up by fruit 
trees and by root crops than the nitrogen of sulphate of ammonia; 
but I have tried the two in comparison with each other five 
or six times on fruit trees and root crops in this country, and 
find that this superiority does not exist here; in fact, if any- 
thing, the nitrogen in the sulphate of ammonia gives the better 
results. We do not, therefore, need to use nitrate of soda here. 
But there are also other sources of nitrogen, as shown in the table 
at the end of this lecture. : 
It will be seen from this table that nitrogen is obtainable in 
sulphate of ammonia, nitrate of soda, dried blood, dried offal, and 
also mixed with other things in dried night-soil, farm and stable 
manure, and compost heaps, and in smaller quantities in dried fish, 
‘some kinds of guanos, and bone dusts and meals. 
* Since the above statement was made it has been offered at £12 10s. per ton. ’ 
