318 TALKS ON MANIRES. 



"Sulpluiric acid has a stronger aftiaity for lime tlian phosphoric 

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

 three-lime phosphate, to take away two atoms of lime, you get t.iC 

 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 tlio 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, 142. 



" An average sample of commercial bone dus"t," continued the 

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

 take 020 lbs. of finely-ground bone-dust, containing 310 lbs. of 

 three lime jthosphati', and mi.\ with it IGO ll>s. of sulphuric acid 

 (say 240 lbs. common oil of vitriol, sp. gr. 1.7), the sulpiiuric acid 

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

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



"And that will give j'ou," said the Deacon, " 780 lbs. of 'dis- 

 solved bones,' or superphosphate of lime." 



" It will give you more than that," s.iid the Doctor, " because, as 

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

 atoms (oG lbs.) of water. And, furthermore, the two atoms of 

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

 The mi.vture, therefore, contains, even wlien perfectly dry, 72 lbs. 

 of water." 



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



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

 whic'ii Mr. Lawes used in his experiments was made on the farm 

 from animal cliarcoal, or burnt i>on:s, ground as fine as jtossible — 

 the tlner tlie better. We took 40 lbs. of the meal, and mixed it 

 witli 20 lbs. of wafer, and then poured on 30 Ib.s. of common sul- 

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

 and then threw it out of the vessel into a heap, on the eartli-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 lbs. bone-meal, 30 lbs. v.-ater, and 30 

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

 the acid and meal together easier and better." 



"Dr. Ilabirshaw tells me," said tlie Doctor, "that in making 

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

 is used. The water in tlie txuano and in the acid is sufficient to 



