206 On Superphosphate of Lime. 



up to the standard so fixed, and has fair ground of complaint if it 

 should be inferior, whether that inferiority proceed from adultera- 

 tion or otherwise. 



But if we were in difficulties about guano — a substance which 

 was simply imported in its natural state — the tampering with or 

 altering which constituted an act of adulteration, how much less 

 satisfactory must be the trade in superphosphate of lime, which has 

 at present no definite or fixed composition, and which may be of 

 better or worse quality, according to the integrity and skill or the 

 cupidity and ignorance of the manufacturer — for it is to be 

 remembered that the term superphosphate of lime, in its present 

 application, does not refer to a pure chemical substance containing 

 known proportions of different ingredients, but to very various 

 products having little in common but the name. 



At present, therefore, it rests entirely with the manufacturer to 

 decide what shall be the composition of the substance which he 

 sells under the name of superphosphate of lime ; and so little 

 judgment and knowledge is in some cases employed in its manu- 

 facture, that I have several times met with samples of the manure 

 containing no portion whatever of the substance it was intended 

 to supply. Even with the best intentions on the part of the 

 maker there is some little difficulty in obtaining a good article, 

 and any error in the substances employed or in the mode of mixing 

 them may easily lead to a very unsatisfactory result. 



My object in the present paper is to point out what superphos- 

 phate of lime is : to give the composition of all those substances 

 which are or may be used in its manufacture ; to furnish approxi- 

 mative formulas for the use of each of them ; and finally, by 

 showing what actually is, to indicate what should he the average 

 composition and value of a fair market sample of this manure. 



By this course I may hope to benefit the farmer in two ways : 

 by enabling those who wish to do so, to take advantage of the 

 different materials available for the making of superphosphate for 

 their own use, and by affording to the less informed maker who 

 is honestly anxious to produce a good manure, that amount of 

 acquaintance with the subject which shall ensure his success. In 

 so doing, I do not think it necessary to enter into a history of the 

 manure, or to refer to the practical results that have been obtained 

 from its use, and I shall confine myself to the chemical part of 

 the subject, apd to the principles which are involved, fully satisfied 

 if, by so doing, I am able to raise the standard of its general 

 manufacture to the perfection at which the best makers have 

 already arrived, and of its use to that of the most intelligent 

 turnip growers of this country. 



There are several compounds of phosphoric acid and lime 

 known to chemists, but of these two only in any way concern us 



