. 
¥ 
J. I. Smith on determining the Alkalies in Minerals. 565 
a yellow deposit soon takes place, which by the microscope will 
be seen to consist of octahedral crystals of the double chlorid of 
potash and platinum: the evaporation should be continued very 
gently with a heat not exceeding 120° to 130° until the liquid 
begins to dry on the edge; if this be now examined under the 
microscope, and soda be pres- 
ent, beautiful needle-shaped 
crystals will be seen, both 
formed and forming, with an 
oblique angle of termination, 
resented in the figure. The 
border of liquid on the glass 
is the place to observe these 
crystals, and that, while the 
process of drying is going on. 
When the amount of soda is 
very small, it is best to allow 
the solution on the glass to ‘ 
dry in the slowest possible manner. Should the quantity of soda 
be still smaller or the nature of the crystals doubtful, resort may be 
had to polarized light, when the prismatic crystals of chlorid of 
platinum and sodium will be at once rendered visible by their 
beautiful colors, as they possess polarizing properties, whereas the 
crystals of chlorid of platinum and potassium, besides differing in 
form, do not polarize light. 
38. This method of detecting a small quantity of soda in the 
presence of potash, I have employed since June, 1850, while en- 
gaged in the examination of the collection of urinary ealeuli 
belonging to the Dupeytren museum at Paris; at that time, it 
Was employed daily in the laboratory of Messrs. Wurtz and Ver- 
deil; the special reason for devising it was to examine the nature 
of the trace of alkali almost invariably found in the uric acid cal- 
culi after combustion. 
39. The reason for making special reference to the date of the 
original employment of this method, is to claim priority in its use, 
as Mr. Andrews announces it in a late number of the Chemical 
Gazette as a new method. Were not the method so well known 
and so constantly employed in the laboratory of Wurtz and Ver- 
deil at the period above mentioned, I should not now set up any 
reclamation in the matter. : 
_ 40. The amount of soda that can thus be detected, is exceed~ 
ingly small, as the liquid can be concentrated to the very smallest 
bulk. When the amount of potash is proportionally large com- 
pared with that of the soda, it is better to put the chilorid - 
platinum in a drop of the solution of the alkaline ehlorids placed 
