GUANO. 197 



Exceptions to this rule may, however, occur, when 

 a guano contains many soluble mineral salts. Spe- 

 cimens have been met with in commerce, which con- 

 sisted to the extent of one half or two thirds of sea- 

 salt and Glauber salt ; such guanos, upon being treat- 

 ed with hot water, would only leave a residue of from 

 one to two drachms of insoluble substances, yet 

 must, nevertheless, be regarded as any thing but good 

 merchandise. In such a case most complete secu- 

 rity is afforded against an erroneous decision by the 

 use of the combustion test described above (p. 193) ; 

 for then it would be found that a guano of the kind 

 in question yields three drachms and more of ashes, 

 and must accordingly be admitted as an inferior va- 

 riety. 



5. Vinegar Test. Pour strong vinegar over the 

 guano to be examined, or, better still, some muriatic 

 acid ; if a strong effervescence ensues, an intentional 

 adulteration of the guano with lime may be inferred. 

 This substance may also be recognized by the com- 

 bustion test, since lime remains behind in combus- 

 tion and augments the quantity of ashes. 



On the best sources for obtaining guano little pos- 

 itive information can be given, since bad and good 

 varieties may both be carried everywhere alike, and 

 since admixtures and adulterations may be made in 

 every place. Good Peruvian guano can only come 

 to Europe through a single English firm (Gibbs, 

 Bright, and Company, London), who have concluded 

 17* 



