STATE GEOLOGIST. 119 
containing 3 grams of sodium carbonate and 0.1 gram of caustic soda. 
After heating the liquid, decant again through the same filter. Repeat 
until no more silicic acid is found in the filtrate. Usually four washings 
are sufficient. Then transfer the residue to the filter which has done 
service throughout this analysis and wash with hot water, acidulated with 
hydrochloric acid. Finally finish the washing with a Io per cent. solution 
of ammonium nitrate. If the filtrate should become turbid, the addition 
of a little ethyl alcohol usually prevents the running through of the fine 
matter of the residue. Ignite and weigh the insoluble residue. 
Mix the insoluble residue with eight times its weight of sodium 
carbonate, fuse and determine the silica as usual. In the filtrate from 
the silica precipitate the iron and alumina and weigh as in the regular 
analysis. 
We can now calculate the amounts of clay substance, quartz and 
feldspar as follows: One gram minus the weight of the insoluble residue 
multiplied by 100 gives the per cent. of clay substance and all other 
minerals soluble in boiling sulphuric acid, like mica, hornblende, car- 
bonates of iron or calcium, etc. The per cent. of silica in the insoluble 
TESIGUE TMS B52 times We Wem Clr Une allesinime, gerne 
ferric oxide in the insoluble matter multiplied by 100 will give the 
per cent. of quartz, while the weight of the insoluble residue minus the 
weight of the quartz as just calculated times 100 will give the per cent. of 
feldspathic matter. The constant 3.52 is obtained from the typical anal- 
ysis of orthclase feldspar and is equal to the ratio between the per cent. of 
silica and the per cent. of alumina, which are 64.76 and 18.4, respectively. 
This method of analysis can make no claim to scientific exactness, 
but gives a close approximation to the actual mineral composition of white 
burning or kaolin-like clays. It does not give equally exact ideas, as to 
the constitution of the impure red-burning clays and shales, chiefly be- 
cause the minerals taken into solution by sulphuric acid are numerous 
and the matter thus classified as clay substance, bears little resemblance 
to the constitution of real kaolinite. 
This method, though giving extremely valuable data in regard to the 
mineralogical character of a clay, yet neglects to give expression to the 
coarseness or fineness of the grains composing the matter insoluble in 
acid, and hence fails to indicate the readiness with which the clay unites 
with lime to form silicates and aluminates. In order to overcome this 
to a certain extent, a mechanical analysis would have to be made of 
the insoluble residue, which, however, would still fail to tell just which 
of the various sizes are feldspar and which quartz. Lime can decompose 
and unite with the constituents of feldspar, the latter being a silicate, with 
far greater ease than with quartz, both being assumed to have the same 
size of grain. Hence we see that the ordinary rational analysis is defi- 
cient and does not produce exactly the kind of data desired. 
