STATE GEOLOGIST. 1237 
By 75 minutes is meant the time during which the sample is exposed 
to the temperature of 1100° C., which of course means a much longer 
burn, since one hour elapses before the furnace can be raised to 1100". 
There can be little doubt but that the time thus allowed is ample to 
accomplish the intended result. It is well known that for the complete 
decomposition of silicates in the alkali determination, a heating of 50 
minutes over a Bunsen burner is sufficient, the temperature of which 
certainly does not exceed 1100”. 
Having thus arrived at standard conditions of burning which, in 
the nature of the case, are bound to be more or less arbitrary, it was 
decided to apply this method to typical constituents of clay, prepared in 
several well-graded sizes. For, by knowing the action of lime upon each 
of these materials and for each of the several sizes of grain, it is possible 
for us to obtain a more definite idea of the character of the more inert 
constituents of clay, not readily available for hydraulic purposes. Of 
course, we can say in general that as particles of quartz feldspathic and 
micaceous minerals are coarser, the more resistant will they “prove 
to the action of lime, yet we do not know just to what extent the chemical 
action of lime is affected by the size of grain. 
For this reason two series of experiments were carried out in which 
quartz and feldspar grains were burned together with lime in a mixture 
containing 80 per cent. of the calcium carbonate, the heat being main- 
tained for 75 minutes at a temperature of 1100° C. 
The quartz taken for this purpose was pure quartzite which was 
crushed and graded to the sizes by sieving. Six sizes. were adopted, as 
follows: 
Grains between 150 and 120 mesh sieve. 
Grains between 120 and 100 mesh sieve. 
Grains between 100 and 80 mesh sieve. 
Grains between 80 and 60 mesh sieve. 
Grains between 60 and 40 mesh sieve. 
Grains between 40 and 20 mesh sieve. 
Se EN hm SY ES 
In addition to these sizes, there was included in the series a ground 
flint, as sold to potters, which is quartzite ground to a fine powder in 
ball-mills using flint pebbles. 
After being mixed with CaCO, in the condition of a slip, the mixtures 
were evaporated to dryness and made into briquettes which were burned. 
On making the rational analysis the mesulls obtained were as shown 
in the following table: 
Sizes. | Ground 150-120] 120-100} 100-80 | 80-60 | 60-40 | 40-20 
Per cent. residue.....| 28.83 | 63.8 | 78.53 | 86.52 | 86.27 | 93.78 | 96.83 
Per cent. taken in so- =| 
LUbLOM ae. eee: | Mie lO Oe al ile A(e len 4 Sa e728. Gala aley 
