Mr. Warington on Preserving Salts for the Microscope. 505 



be perfectly pure; it was therefore digested in weak solution 

 of ammonia, which dissolved the whole, with the exception of 

 a small quantity of brown powder, which was found to consist 

 of 0*06 gr. of peroxide of iron and a trace of gold. The am- 

 moniacal solution was precipitated by nitric acid, and gave 

 0*52 gr. of chloride of silver. The solution (A) was next 

 precipitated by solution of chloride of sodium, and gave 10'25 

 grains of chloride of silver, equivalent to 7*66 grains of silver ; 

 solution of caustic potash, and boiling threw down the oxide 

 of copper, and yielded 0*30 gr. oxide of copper = 0'24 gr. of 

 copper. Thus we have — 



Silver 7*66 grains. 



Chloride of silver. . . 0'52 



Copper 0*24 



Oxide of iron. . . . 0*06 



Gold a trace 



8*48 

 Loss . 0*02 



8-50 



It becomes a curious question as to the origin of this chlo- 

 ride of silver, which was evidently the superficial grayish film 

 observed under the microscope, and which partially separated 

 in the act of bending the metal after heating. That it must 

 have been produced by the continued action of chlorides, per- 

 haps aided by sulphates present in the brick clay from which 

 the vase was excavated, there can be little doubt, and the per- 

 oxide of iron also existing in the clay may have assisted this 

 action. 



The passage of the metal to the brittle state in this and in 

 all other cases will, I think, be found attributable to some 

 electrical action arising from sudden cooling, vibration or 

 concussion, chemical action, &c. to which the metallic body 

 or alloy may have been exposed. 



LXXIV. Note on a Means of Preserving the Crystals of Salts 

 as permanent objects for Microscopic Investigation. By 

 Robert Warington, Esq* 

 tTAVING occasion lately to require the crystals of various 

 •*--*■ salts in a state fitted for examination by polarized light 

 under the microscope, and as the preparation of these crystals 

 was frequently attended with much trouble and loss of time, 

 it became a point of importance to render the object, when 

 once perfected, permanent, so that the investigation of certain 

 individual crystals could be repeated, and additional obser- 



* Communicated by the Chemical Society; having been read January 

 15, 1844. 



