4 THE TROPICAL AGRICULTURIST. [July 1, 1903. 
however beneficial it may be in the m&jority of 
instances, has in some soils led ^to the complete or 
partial failure or the presence of disease in the turnip 
crop. 
"No acid combination as such can enter into plants 
without doing them serious damage ; even free vegeta- 
ble acids, as humic and nlmic acids, are injurious 
to all crops cultivated for food for the use of man 
or beast ; and unless these acids, which are always 
present in wtiat practical men so call humus, are 
neutralised by lime, or marl, or earth, none but the 
roughest and most innutritious herbage can be grown. 
Free mineral acids, are I believe still more injurious 
to all farm crops, and perhaps to all plants, than 
the free organic acids that are found in humus. A 
very dilute solution of sulphuric acid — say one part 
in 1,000 of water— may be used with advantage for 
killing grass in gravel walks made with flint or quartz 
Band ; after one or two applications, the weeds will 
be destroyed and will not reappear for a long time. 
But if the walks are made with limestone gravel, 
the application of a much stronger acid has little 
or no effect on the grass or weeds ; after some time 
tha hater seem to grow all the better for having 
had a t;;,ste of dilatt sulphuiio aoid. lu reality, 
however no acid enters these plants, but on coming 
into contact with the limestone gravel, unites with 
the lime to form that useful fertilizer, sulphate of 
lime or gypsum. These examples thus prove un- 
mistakably that a soil vihich contains free acid, 
in ever eo small a quantity is unfit to maintain a 
healthy growth. We have therefore, strong pre 
sumptive evidence that soluble phosphate, a combi- 
nation which has a strongly acid character, does 
not as sucli enter the roots of plants. The recon- 
version of soluble into insoluble phosphate, perhaps 
may appear undesirable, but in reality, it is not only 
beneficial, but absolutely necessary to the healthy 
and luxuriant development both of turnips and all 
other crops to which superphosphate is applied. 
The more rapidly and completely the soluble phos- 
phate in commercial superphosphates and turnip 
manures, is precipitated and rendered insoluble in 
the soil, the move energetic will be its effect upon 
the turnip crop.'' 
The above statements, made nearly 40 years ago, 
represent the views of one who was rightly regarded 
as an authority upon the properties and use of 
artificial manures, and it is interesting to note the ex- 
tent to which these views have been realiaed in actual 
farm practice during succeeding years. 
NEUTBAL PHOSPHATES. 
In 1875, the Aberdeenshire experiments with finely 
ground phosphates were instituted and conducted 
under the manngemeut of Professor Jamieson for 
some years. The publication of the results excited 
much interest, for they demonstrated by actual field 
experiments that iusoiuble, or more properly termed 
undissolved, phosphates, if applied in a finely-ground 
condition and in sufficient quantity, possessed very 
considerable fertilising value, whereas, according to the 
previously held theory, such raw phosphates were 
supposed to possess no practical manurial value. 
Further, these experiments proved that on cert.iin 
soils deficient in lime, ordinary soluble phoaphate 
was not superior in its action as a manure to undis- 
solved phosphates to anything like the extent that 
had hitherto been geutraily supposed. 
Very naturally these novel results, being opposed 
to the theory hitherto held, excited a considerable 
amount of hostile criticism which however time 
and more extended experience has proved to have 
been unreasonable and erroneous. 
The experiments were earned out at five stations 
situated in different parts of the couuty oi Aberdeen, 
and the soils ate described in the official report as 
being " black mould resting upon a granite subsoil," 
and the analyses show that in every case they were 
specially deficient in lime. The figures for lime at 
these five stationa were respectively '08— 'l?— 12— 
•33 and '38 per 100 parts of the dry soil. 
These soils were in fact exactly those upon which 
soluble phosphate as supplied by superphosphate 
would not be likey to exert its full benefit, while the 
vegetable acids existing in the black mould would 
naturally dissolve the fiuely ground mineral phos- 
phate to a very considerable extent. In short the 
conditions were most favourable to the action of an- 
dissolved phosphates, and most unfavourable to the 
action of dissolved or soluble phosphates. 
The experiments in themselves, were however, dia- 
tinctly useful both scientifically and practically and 
Professor Jamieson will always be favourably asso- 
ciated with what must now be regarded as a step 
forward in the economical application of finely ground 
neutral phosphates. 
ALKALINE PHOSPHATB OR BASIC SLAO. 
About the year 1883 the now well-known basic slag 
or Thomas phosphate powder was introduced to the 
agricultural world. It is the residual slag resulting 
from the treatment of iron ore by the Thomas- 
Gilohrist process of adding lime in order to removo 
the phospiioric acid and silica. Briefly it consists of 
basic phosphate of lime and basic silicate of lime 
associated with some iron, manganese and magnesia 
compounds. 
It has a distinctly alkaline character, but it is a 
mistake to suppose that this material contains any 
considerable quantity of free lime, because any such 
excess of lime would indicate a wasteful method of 
manufacture, lime being only added in sufficient 
quantity to remove the phosphorous and silica existing 
in the original iron ore. Though but slightly soluble 
in ordinary water, it dissolves to a certain extent in 
water impregnated with vegetable acids, and it is 
the neutralisation of such acids which exist in sour 
grass that largely contributes to make its application 
so beneficial on certain kinds of soil. No other 
manure has ever before occasioned so great a diversity 
of opinion as to its value as a fertiliser. When finely 
ground and applied to suitable land with sufficient 
water either in the soil or from rainfall, the results 
have been most satisfactory, both in the increased 
yield and in the improved quality of the grass and 
hay ; but where the conditions are unfavourable and 
the land unsuitable, the results have been most dis- 
appointing. Indeed, when first introduced agricultural 
chemists of high repute were disinclined to place any 
fertilising value on such a hard fused mass, however 
finely it might be ground, because it was so insoluble 
in ordinary water. Little by little, however, farmers 
were induced to take small quantities for trial, 
chiefly on old and sour grass lands and the practical 
results were so good on certain soils— rich in vege- 
table acids but poor in lime— that scientific authorities 
were soon compelled to recognise its value, and aa 
the market price was low the material naturally 
became popular in certain localities. In this country 
the importance of fine grinding has hitherto been 
recognised as the chief test of the probable manurial 
value, but in Germany, Professor Paul Wagner, of 
the Agricultural Station of Darmstadt, has insisted 
upon the solubility in a 2 per cent, solution of vege. 
table acid, such as citric acid, as a further and more 
definite test of probable manurial value. 
Dr. Bernard Dyer, in his paper " On the Determi- 
nation of Probably Available Mineral Plant Food in 
Soils" ("Journal of the Chemical Society," 1894), has 
adopted a cold 1 per cent, solution of citric acid for 
determining the proportions of phosphoric acid and 
potash existing in a presumably available form in 
the soil. 
The present writer, however, has selected as his 
standard solvent a 010 per cent, cold solution 
consisting of 1 part of citric acid to 1,000 parts of cold' 
distilled water. Such a solution is twenty times 
weaker than that of Professor Wagner and ten times 
weaker than that of Dr. Dyer. la fact, it represents 
