260 Dr Davy's Miscellaneous Observations^ 



almost transparent, — jelly-like. — owing to the excessive mi- 

 nuteness of its particles, individually out of the limits of dis- 

 tinct vision, using the best microscopes at present construct- 

 ed. The precipitate of phosphate of lime is less transparent, 

 consisting as it does of granules of a larger size, and within 

 the limits of microscopic observation. The precipitate of 

 phosphate of magnesia in the form of the double salt ; the 

 ammoniaco-magnesian phosphate, is almost of an opaque 

 white, being thrown down in crystals which reflect a good 

 deal of light. Though a tolerable conjecture may thus be 

 formed of the nature of a precipitate by ammonia, and that 

 whether pure or mixed, it will be right in most instances, 

 and of course always when perfect accuracy is aimed at, to 

 trust only to the appearances as a guide to the use of appro- 

 priate distinctive tests. 



7. If the pulp of the tamarind, including the seed, be ex- 

 posed to the air, it remains moist for a considerable time. It 

 is not attacked by insects, nor does mildew soon form on it. 

 If it be digested in water, and the solution formed be sepa- 

 rated by filtration and evaporated, an extract is obtained pos- 

 sessing similar properties. It deliquesces in a moist atmos- 

 phere, probably owing to the presence of magnesia in combi- 

 nation with one or more vegetable acids, for I have found 

 this earth in a notable quantity, in the pulp which I have ex- 

 amined. Whilst the entire pulp, and the residue from it, are 

 so little liable to change, the residue is otherwise. If ex- 

 posed to the air, it soon loses all excess of moisture, and is 

 rendered dry. If kept in water and exposed to the air, it 

 soon becomes covered with mildew. Does not this show that 

 the acid and saline matter of the pulp have a preservative 

 quality, and are designed for the purpose of preservation \ 

 The instance adduced appears to me a striking one. Very 

 many more might be pointed out of similar significancy ; in- 

 deed, it would be more difficult to find an example of the 

 contrary. The preservative materials in the vegetable king- 

 dom, especially in the instance of seeds, appear to be chiefly 

 woody fibre, forming husks and shells ; oils, as in the instance 

 of certain kernels or nuts, and sugar and acid salts in the 

 instance of certain fruits ; and, as in the example of the tama- 



