the form of sulphate of ammonia for 30 years, and are now in such acid
condition that no crops thrive upon them. The corrective, of course, is
lime, and if ammonium sulphate were somewhat lower in price, its use
would be profitable, justifying cost of correction of acidity if it
should occur. It is used by manufacturers of commercial fertilizers,
and is well adapted to mixtures on account of its physical condition.

Dried Blood.--There is no more satisfactory source of organic nitrogen
than dried blood of high grade. The best blood, red in color, contains
nearly as much nitrogen as nitrate of soda, running from 13 to 15 per
cent. The nitrogen is not as quickly available as that in the nitrate,
but is more so than that in any other form of organic nitrogen. One
would rarely go amiss in the purchase of dried blood as a carrier of
nitrogen if the price were relatively as low as in the case of nitrate
of soda, but he should not let any prejudice in favor of animal origin
of fertilizers lead him to pay an excessive price per pound for the
nitrogen contained in it. Such a prejudice has caused the nitrogen in a
good red blood to sell for one half more per pound than in nitrate of
soda, and it is not a good purchase on that basis.

The lower grades of dried blood on the market contain as low as 6 per
cent of nitrogen, and the animal refuse put into it gives it a content
of a few per cent of phosphoric acid. This black blood is very variable
in composition, and should always be accompanied by a guaranteed
analysis.

Tankage.--The waste from the slaughter of animals goes into a product
called tankage. The refuse is cooked for removal of the fat, and then
ground. It may run high in nitrogen on account of the amount of meat in
the mixture, and it may be low in nitrogen and very high in phosphoric
acid by reason of the large amount of bone in the mixture. Only a
guarantee of analysis affords safety to the buyer. It is a relatively
slow and good fertilizer, and is used usually in connection with forms
of plant-food that are more quickly available.

Fish.--Near the Atlantic coast a large quantity of ground fish, after
the extraction of oil, is used as a fertilizer, but the cost of the
nitrogen and phosphoric acid in this carrier is relatively too high to
justify its free use. Like dried blood, its organic character gains for
it a popularity that does not have full justification in fact.

Animal Bone.--The original source of phos