0?2 Guano. 



307 



nia even at the ordinary temperature of tlie atmosphere, and 

 assume the condition of the powdery portion with which they are 

 mixed. 



1. The quantity of sand contained in a portion of the powdery 

 variety I found to amount to nearly 1 1 per cent. ; while in one 

 lump there were present 8 per cent., and in another less than 

 2 per cent. The sand consisted chiefly of mica, quartz, and fel- 

 spar, the debris of the igneous rocks of the coast of Peru. Occa- 

 sional fragments of rock occur, of considerable size also, among 

 the guano. 



2. The quantity of volatile or combustible matters (including 

 the water and ammoniacal salts) which are capable of being- 

 driven or burned off by a red heat is also very variable. Thus, 

 4 portions, taken at random from different parts of the box, lost, 

 respectively, 23 1, 46, 60, and 53 per cent, of their whole weight; 

 leaving an ash of a white or slightly grey colour. This difference 

 is not owing to the presence of unlike quantities of sand, for the 

 numbers above given are calculated on the supposition that the 

 specimens were all free from sand. Thus the first specimen lost 

 by heating only 21 J; but, as it contained 8 per cent, of sand, it 

 would have lost, as stated above, if free from sand, 23J per cent. 



In so far- as the volatile constituents are concerned, therefore, 

 the guano which comes to this country may vary in value from 

 1 to 3. 



3. Yet the loss by heating, which is very easily ascertained, is not 

 a true measure of the richness of the guano in ammonia and other 

 valuable organic matters. When reduced to powder it rapidly 

 absorbs moisture from the air. Thus, in 48 hours, a weighed 

 portion of a lump broken into coarse powder gained by exposure 

 to the air 2 per cent. ; another portion gained in 10 days no less 

 than 6 per cent., and after a longer time it became perceptibly 

 moist between the fingers. This absorption of water from the 

 air will tend not only to depreciate the value of a given weight of 

 the guano when brought to our humid climate, but also to cause 

 errors in the results of agricultural experiments made with dif- 

 ferent samples of the manure. 



4. I have stated above that the lump guano when crushed 

 gives off ammonia at the ordinary temperature of the atmosphere. 

 In hot weather this may be rendered sensible by holding over it 

 a feather dipped in strong vinegar or diluted muriatic acid (spirit 

 of salt), when white fumes will be perceived; or at any time by 

 heating the guano to 100° or 150°. By this evolution of ammo- 

 nia it loses both in weight and in virtue. By drying at 150° I 

 found a lump to lose 1 1 per cent, of its weight, ammonia being 

 sensibly given off during the whole duration of the experiment ; 

 yet when it was again exposed to the air it absorbed so much 



z 2 



