358 CHEMISTRY. 



raense quantities of it in different parts of the earth. It is 

 calculated that the deposits of it in South and Middle Peru 

 amount to more than twenty millions of tons. The value 

 of this manure, when it is good, is very great. Its good- 

 ness depends upon the amount of nitrogen it contains lock- 

 ed up in its ammonia. Next to nitrogen, phosphoric acid, 

 contained in phosphate of lime, must be considered as the 

 most valuable constituent of guano ; but of so much more 

 value is the nitrogen than this, that we may lay it down as 

 a rule that the more of ammoniacal salts and the less of 

 phosphate of lime guano contains, the higher is its value. 

 Peruvian guano is better on this account than the guano 

 of Patagonia and that of Africa. The reason that these 

 latter have so small a proportion of ammoniacal salts in 

 them is that by exposure to the action of air and water 

 these salts have been to a great extent washed out. Guano 

 is deficient in potash, and therefore in its application wood- 

 ashes make a useful addition. 



500. Tests of Guano. Guano varies much in its char- 

 acter, and on account of its pecuniary value is often adul- 

 terated, hence it is well that certain plain tests of its chem- 

 ical composition should be known, that they may be applied 

 by buyers of the article. We will mention some of them. 

 1. Test by Combustion. Put fifteen grammes of the guano 

 to be examined in an iron spoon, and hold it over some red- 

 hot coals until a white or grayish ash is left. The weight 

 of the ash, subtracted from that of the guano, gives you 

 the proportion of nitrogenous substance, for this has been 

 burned tip and volatilized, while the phosphate of lime 

 makes the ash. In this application of heat the odor differs 

 according to the character of the guano. That from a good 

 specimen is pungent, like the vapor from spirits of harts- 

 horn, while the odor from a poor specimen is like that of 

 singed hair. 2. Lime Test. Put a teaspoonful of guano 



