866 QUEENSLAND AGRICULTURAL JOURNAL. [1 Nov., 1898. 
slags varies from 80 to 90 per cent. of the total phosphoric acid, the consumer 
should purchase a high-grade Thomas’ slag—z.c., one containing the highest 
possible percentage of phosphoric acid soluble in citric acid. : 
In addition to this quick-acting phosphoric acid, Thomas’ slag also contains 
some that is dissolved more slowly, the effects of which are felt even after some 
time; this fact is of especial importance in the case of arboreous plants. 
Another beneficial effect is produced by the high percentage (30 to 50 per 
cent.) of lime contained in Thomas’ slag, a matter which is especially worthy 
of consideration with soils deficient in this ingredient. 
8. Bone-meal (steamed bones) is very slowly decomposed in the soil, 
and, according to the latest investigations, produces a much less marked effect 
than Thomas’ slag, though formerly the contrary was believed to be the case. 
Steamed bone-meal is, therefore, used only when it is intended to enrich the 
soil permanently. Bone-meal is decomposed in the same manner as acid 
phosphate, in order that the phosphoric acid it contains may be made available 
in the form of water soluble phosphoric acid. 
ITI. Porasstc Kervrmisers. 
The potash contained in the ashes of plants is a very good source of this 
ingredient. However, ashes are placed upon the market in such limited quan- 
tities that they do not require special attention, except in rare instances. ‘The 
principal sources of potash, which is one of the essential plant-food ingredients, 
are the Stassfurt potash salts; these are placed upon the market in the follow- 
ing forms :— 
1. Crude potash salts, being the natural products of the mines. These 
are furnished in a finely ground state as carnallit, kainit, and sy)vinit. In 
addition to muriate or sulphate of potash, they contain magnesia salts and 
chloride of sodium (common salt) ; these latter, however, as a rule, possess but 
little value for plant-nutrition. 
The acids (muriatic and sulphuric) must first be converted in the soil witl 
the aid of lime, and, together with the by-products, worked into the deeper layers, 
in order that the crude salts may be made available. The effect of the crude 
potash salts is, therefore, primarily shown in changing the condition of the 
top soil. The salts absorb moisture from the air, and thereby make the soil 
moist and compact; this is very valuable in the case of light dry soils, less 
so in the case of heavy soils. Great caution should be exercised in the appli- 
cation of crude salts to sensitive plants; they injure the burning quality of 
tobacco and decrease the percentage of sugar in sugar-cane. 
On the other hand, crude salt should be applied to plants that consume 
large quantities of salt,such as cocoanuts; also when it is desired to combat 
insect-pests, as in cotton. The crude potash salts are preferable to common 
salt for this purpose, as they supply at the same time one of the essential 
plant-food ingredients, thus serving a double purpose. When the products 
have to be procured from a distance, kainit and sylvinit—the latter, as a rule, 
contains the larger percentage of potash—are preferable to carnallit, as the 
last-mentioned salt is not only poorer in potash but very readily absorbs 
moisture. Howeyer, as a rule, the application of refined potash salts is more 
advantageous, as they are much purer, and contain a larger percentage of 
potash (four to five times as large). On account of the high freight charges 
to the colonies, the 1 1b. of pure potash is cheaper in the refined than in the 
crude salts. 
2. The sulphates, such as sulphate of potash and sulphate of potash- 
magnesia, have been successfully applied to all plants, especially to those in 
which the quality of the yield is of prime importance—e.g., tobacco, sugar-cane, 
tea, pineapples, and oranges. 
3. In all other cases muriate of potash should be employed; it offers the 
advantage of being somewhat cheaper than the sulphates, while the effect is 
the same, especially as regards the quantity of the yield. 
