462 



Dr. G. Harley and Mr. H. S. Harley. [Mar. 22, 



permitted to remain in the solution. When taken out they rapidly dry 

 and shrivel up. We shall take occasion to point out in our next 

 communication, which will be on the microscopic structure of pearls, 

 that a decalcified crystalline pearl bears an intimate resemblance to a 

 decalcified bone, in so far as it possesses a perfectly organised matrix 

 of animal matter. ISTo phosphates whatever were found in any of the 

 three before-named varieties of pearls.* 



The next point being to ascertain the exact proportions of the sub- 

 stances composing the pearls, and pure white pearls being expensive, 

 from our having ascertained that all the three kinds we were operat- 

 ing upon had exactly the same chemical composition, instead of making 

 separate quantitative analyses of them, we simply selected two pearls 

 from each variety, of as nearly the same size and weight — giving a 

 total of 16 grains — and analysed them collectively, the result obtained 

 being — 



Carbonate of limef 91'72 per cent. 



Organic matter (animal) .... 5*94 ,, 



Water 223 



Loss Oil „ 



100-00 



From this it is seen that notwithstanding that mother-of-pearl 

 consists of precisely the same ingredients, their proportions are quite 

 different from what they are in fine, pure white pearls (we say fine 

 pure white, because pearls vary greatly in purity, and those we 

 analysed were good ones), which are infinitely denser, and con- 

 sequently harder than the mother-of-pearl constituting the shells in 

 which they are formed. The analysis of mother-of-pearl given in 

 Watts' ' Dictionary of Chemistry ' is — 



Carbonate of lime 66 '00 per cent. 



Water 31 '00 



Organic matter 2*50 „ 



thus showing that while mother-of-pearl contains less than half 

 the quantity of organic matter pearls do, it at the same time possesses 

 close upon fourteen times more water. This fact appears to us all 

 the more surprising as, not alone to the naked eye, but even under the 



* Phosphates are referred to as being present in pearls by Eudler in his article in 

 the ( Encyclopaedia Britannica.' 



f The carbonic acid was estimated by disengaging it with dilute sulphuric acid 

 into a soda-lime tube, and calculating the increase in weight (as described by Lunge 

 and Hurter in ' The Alkali Maker's Pocket-book ') . The amount of the organic matter 

 by noting the loss by weight after calcining — slightly moistening the mass with a 

 solution of ammonium carbonate. 



