“STATE GEOLOGIST. 177 
The following conclusions may be drawn from Nauss’ work: 
First. In regard to the decomposition of calcium carbonate, it is 
clearly shown that it begins to break up between 610° and 650° C., and 
before 700° is reached the evolution of carbon dioxide is going on quite 
rapidly. At 1000° the evolution is practically at an end. 4 
Second. On examining the amounts of insoluble residue and com- 
paring the percentage with the known amount of quartz in the mixture, 
18.66 per cent., and making allowance for the small amount of quartz 
in the kaolin itself, it is seen that the kaolin is decomposed completely 
at 850° C. and almost completely at 800° C. 
Third. Free quartz seems to be attacked by the calcitum oxide soon 
after the completion of the decomposition of kaolin, probably at about 
g50° C., which reaction continues at an increasing rate up to the highest 
temperature employed in these experiments. It is quite evident, also, 
that the length of time of burning influences the amount of quartz 
attacked somewhat, so that by longer burning, at least with temperatures 
over I100°, more quartz may be rendered soluble than in a short period 
of ignition. 
A very interesting fact was brought out by the tendency to dust 
observed with the mixtures burnt at temperatures above 1200°. While at 
1200° the briquettes were hard, at 1250°, they dusted very rapidly, and 
at 1300° almost instantaneously. 
On calculating the formula of this mixture from the composition we 
find it to be 1.77CaO, 0.108AI,O,, SiO,, that is, not quite a singulo 
calcium silicate, and hence might properly be classed within the group 
of natural cements. It is not difficult to understand that the dusting must 
be coincident with a significant molecular change from the condition of 
the loose, friable mixture to a hard body breaking. down at once to a 
powder. Might not this fact indicate that up to 1200° these calcareous 
mixtures are but pozzuolane-like, simple silicates, consisting of silicate 
and free base which on further application of heat become chemically 
more complex and non- or but slightly hydraulic? This view is strength- 
ened by the results of another investigation which has shown that on 
increasing the free silica, with but sufficient base to convert the quartz 
into the active state, the hydraulicity is practically as great as with a 
ereater amount of base. 
Kennedy’s Results.—This subject seems important to the writer, 
since, evidently, all Portland cement must pass through these reactions, 
and it is necessary for the proper understanding of the genesis of these 
cements that we should know something 1 in regard to the initial stages of 
the formation of the hydrolite. 
12-8. G. Bull. 3. 
