Mr. Denham Smith on the Composition of Guano. 123 



object-glass of a telescope were analysed by absorption (which 

 might be done by putting a piece of blue glass before the 

 object-glass), I fancy that some insight into this subject might 

 be gained. I can show, I think, that exactly the same mix- 

 ture of colours may possibly take place in the spectrum pro- 

 duced by diffraction, as in the common prismatic spectrum. 

 Balham, Surrey, December 27, 1844. M. O'Brien. 



[To be continued,] 



XII. 0« the Composition of some varieties of South American 

 Guano ; with the description of a new mode of estimating 

 Ammonia, and of a process for separating Lime from Mag- 

 nesia, when these earths exist iii combination with Phosphoric 

 Acid. By 3. Denham Smith, Esq.* 

 T^HE results of the following examinations of guano, ne- 

 ■^ cessary as a matter of business to myself, may prove of 

 some interest to the Society, as they serve to confirm, in most 

 points, those arrived at by previous analysts, especially with 

 respect to the variableness of the composition of this substance. 

 "When I commenced these analyses I had but one sample of 

 guano ill my possession, which came through the hands of a 

 broker in 1842, of the purity of which I could not be certain 

 before analysis., Subsequendy I was successful in obtaining 

 genuine samples of South American guano direct from the 

 warehouses of the importers, the bulks from which these spe- 

 cimens were taken being at the present time in the course of 

 consumption in this country. 



South American guano, as imported, presents itself in three 

 distinct states, although these varieties are often mixed toge- 

 ther in the same bag. The larger proportion of it consists of 

 a damp pulverulent substance of various tints of brown, inter- 

 mixed with nodules, usually of a lighter colour than the pow- 

 der ; some of these nodules are soft, easily crushed by the 

 finger, and often present light brown silky crystals when 

 broken ; others are much harder, of a dirty white and uniform 

 texture throughout. 



The second variety exists as large concretions, often weigh- 

 ing several pounds, presenting various aspects when broken ; 

 sometimes appearing merely to be the first variety in a cohe- 

 rent, instead of a pulverulent state ; at other times as a regu- 

 larly stratified deposit of different shades. 



The third description of guano occurs in irregularly shaped 



masses, very heavy in comparison with the other varieties, and 



* Communicated by the Chemical Society ; having been read May 6, 



1844. On the composition and chemical history of guano, see also Phil. 



Mag. S. 3. vol. xxi. p. 383, and vol. xxiv. p. 317, 395, 470. 



K 2 



