228 



Composition and Value of Guano. 



applies to Peruvian guano. In some varieties of guano which are naturally 

 very wet, all sorts ol' collections and crystallizations have been found, and 

 it excites no surprise that such should be the case; but the experiment 

 just described strengthens the opinion which would be formed from a know- 

 ledge of the circumstances under which Peruvian guano has been pro- 

 duced, and which is, that no amount of separation and rearrangement of 

 the particles could have occurred since its deposition. In " damaged 

 guano," on the other hand, it is easy to trace a crystallization of its salts 

 brought about by the water. 



2. On the Methods of Ancdysis. — First as to drying the specimen. In all 

 our earlier analyses of guano the samples were dried before the com- 

 bustion for nitrogen. It was soon found that this drying could not be 

 effected in the ordinary way. Even at the temperature of the air guano 

 always emits ammonia ; and at 212° the quantity of ammonia is so great as 

 to produce a loss of 2 or 3 per cent, sometimes in the subsequent analysis. 

 To obviate this defect we had recourse to the use of an acid in the drying, 

 A specim.en of the guano in a shallow platinum dish was treated with a few 

 drops of hydrochloric acid, which was allowed to soak through the whole. 

 It was then dried at a water-bath heat without loss, and in the subsequent 

 analysis the presence of the acid had no influence. 



We have subsequently found that a moderately dry specimen of Peruvian 

 guano — that is to say, containing not more than 15 per cent, of water — can 

 be mixed with the soda-lime for nitrogen analysis with perfect safety, with- 

 out drying, provided the soda-lime itself be perfectly dry. The mixture is 

 made in the tube by the help of a corkscrew wire, and no smell of ammonia 

 can be detected. 



In the detailed analyses given in the first Table the substances were 

 separately determined in the same way as the ash of a plant is analysed. 

 One modification of the usual process deserves notice. In burning guano 

 to obtain the mineral part for analysis, a considerable loss of chlorine and 

 sulphuric acid occurs from the escape of these substances in the form of 

 ammoniacal salts. To ascertain the total quantity of the chlorine and sul- 

 phuric acid, it is necessary to saturate the guano with a strong solution of 

 potash or soda, which in the subsequent burning retains the acids in 

 question. 



The following comparison of the corrected and uncorrected results will 

 show the extent of loss due to this cause : — 



The determination of the actual quantity of these ingredients necessi- 

 tates also a correction for the quantity of organic matter as ascertained by 

 burning. In the analyses which are given, in all the tables but the first, 

 the method of examination was as follows : — 



The guano is dried at a water-bath heat and afterwards burnt ; the ash 

 is dissolved in hydrochloric acid, and the solution filtered to separate 

 sand. The earthy phosphates are precipitated by ammonia. This pre- 



