some varieties of South American Guano. 129 



with nitric acid and its loss of weight noted, expressed the 

 quantities of phosphoric acid and chlorine contained in the 

 fused saline residue. To the original solution hydrochloric acid 

 in slight excess was added ; the chloride of silver thus formed 

 was separated, and the clear solution was evaporated with so 

 much diluted sulphuric acid, as would have been sufficient to 

 convert the whole of the fused saline residue into sulphate of 

 soda, had it consisted entirely of chloride of sodium; this eva- 

 poration being very carefully conducted and the residue trans- 

 ferred to a platinum crucible, in which it was heated to full 

 redness until no more acid fumes were given off, the crucible 

 with its contents was accurately weighed, and the weight 

 noted ; if one alkali only was present, its weight was calcu- 

 lated from that of the sulphate ; but if both potash and soda 

 were contained in the specimen of guano under examination, 

 the mixed sulphates thus obtained were dissolved in water, 

 the solution was treated with a salt of barytes in the usual 

 way, and the resulting sulphate of barytes was weighed with 

 the most scrupulous care. The respective weight of each 

 alkaline sulphate contained in the solution was then calcu- 

 lated by the following formula, which I subjoin, as the steps 

 in the calculatio^i are much more readily perceived in figures 

 than expressed in words : — 

 KOSOgBaOSOgKOSOaBaOSOa NaOSOg BaOSOa NaOSOs BaOSOs 



88 : 116 : : 1 : 1-31818 . 72 : 116 : : 1 : 1'61111 

 — 1-31 818 = 0-29293 the difference. Let the weight of the 

 mixed sulphate be 48*54 grs., then 1*318 18 x 48*54 =63-984 

 — 70*525, weight of sulphate of barytes obtained by experi- 

 ment =6-541 -7-0-29293 = 22*33 sulphate of soda — 48-54 = 

 26'21 sulphate of potash, and from these weights the respective 

 proportions of the bases may be calculated*. 



The actual amount of the chlorine or hydrochloric acid, the 

 sulphuric, phosphoric and oxalic acid, of the ammonia, pot- 

 ash, soda, organic matter, &c., contained in the cold aqueous 

 solution, were ascertained by calculation, as well as that of 

 the water. 



The residue insoluble in cold water was then ground to 

 powder, and a known weight of it was boiled with three or four 

 successive half-pints of distilled water, for about an hour after 

 each addition of water ; the mixture was then allowed to depo- 

 sit the undissolved portions, the solution being kept hot during 

 this subsidence and filtered whilst still at that temperature. 

 When water boiled upon this residue came off colourless, and 



• See Phil. Mag. vol. xiii. pp. 132 ct seq. and Barreswil and Sobrero's 

 Ajypendice atu Traites (T Analyse Chimique, p. 41. 



