318 TALKS ON MANURES. 



" Sulphuric acid has a stronger affinity for liine than phosphoric 

 acid. And when you mix enough sulphuric acid with finely ground 

 three-lime phosphate, to take away two atoms of lime, you get the 

 phosphoric acid united with one atom of lime and two atoms of 

 water." 



" And what," asked the Deacon, " becomes of the two atoms of 

 lime ? " 



" They unite with the sulphuric acid," said the Doctor, " and 

 form plaster, gypsum, or sulphate of lime." 



"The molecular weight of water," continued the Doctor, " is 

 18 ; of lime, 56 ; of sulphuric acid, 80 ; of phosphoric acid, 143. 



" An average sample of commercial bone-dust," continued the 

 Doctor, " contains about 50 per cent of phosphate of lime. If we 

 take 620 Ibs. of finely-ground bone-dust, containing 310 Ibs. of 

 three-lime phosphate, and mix with it 160 Ibs. of sulphuric acid 

 (say 240 Ibs. common oil of vitriol, sp. gr. 1.7), the sulphuric acid 

 will unite with 112 Ibs. of lime, and leave the 142 Ibs. of phos- 

 phoric acid united with the remaining 56 Ibs. of lime." 



"And that will give you," said the Deacon, "780 Ibs. of 'dis- 

 solved bones,' or superphosphate of lime." 



" It will give you more than that," said the Doctor, " because, as 

 I said before, the two atoms of lime (112 Ibs.) are replaced by two 

 atoms (36 Ibs.) of water. And, furthermore, the two atoms of 

 sulphate of lime produced, contained two atoms (36 Ibs.) of water. 

 The mixture, therefore, contains, even when perfectly dry, 72 Ibs. 

 of water." 



"Where does this water come from?" asked the Deacon. 



" When I was at Rothamsted," said 1, " the superphosphate 

 which Mr. Lawes used in his experiments was made on the farm 

 from animal charcoal, or burnt bones, ground as fine as possible 

 the finer the better. We took 40 Ibs. of the meal, and mixed it 

 with 20 Ibs. of water, and then poured on 30 Ibs. of common sul- 

 phuric acid (sp. g. 1.7), and stirred it up rapidly and thoroughly, 

 and then threw it out of the vessel into a heap, on the earth-floor 

 in the barn. Then mixed another portion, and so on, until we had 

 the desired quantity, say two or three tons. The last year I was 

 at Rothamsted, we mixed 40 Ibs. bone-meal, 30 Ibs. water, and 30 

 Ibs. acid ; and we thought the additional water enabled us to mix 

 the acid and meal together easier and better." 



"Dr. Habirshaw tells me," said the Doctor, "that in making 

 the ' Rectified Peruvian Guano ' no water is necessary, and none 

 is used. The water in the guano and in the acid is sufficient to 



