On the Jatsalmir Limestone. 
110 
[April, 
water, as may seem necessary. The longer this operation is continued, the more 
perfect will the polish be. 
The grinding and smoothing need only be performed when the stone has to be 
wrought from a rough state. Any two slabs once reduced, may be rubbed together, 
and it will merely be necessary, when they are sufficiently ground, to use the fine 
corundum rubbers, to give the surface the pearly appearance before the polishing is 
commenced. 
Note. — That in making the furrows, when levelling the surface, it is usual, first, 
to corer the stone over with some color, (generally red ochre and water,) that the part 
which has been submitted to the operation of the chisel, may be distinguished from 
that which has not ; in white marble this is indispensable, for those parts which have 
been gone over, cannot otherwise be distinguished, and a good level can never be given 
to any very light colored marble without this precaution. 
The Corundum Rubbers. 
The proportions generally used in making the corundum rubbers, are for the 
coarse, lac 8; corundum 1 : for the medium, lac 12 to 16, and corundum 1, by 
weight. The fine rubber is made by mixing the grindings of agates, cornelians, 
and the like, with lac ; and as the lapidaries’ wheels, upon which they are ground, are 
made of corundum and lac also, the grindings must contain a portion of those 
materials; their proportion, in composition, must vary according to the nature of the 
stone from which they are ground; but 6 of lac, to 1 of grindings, maybe considered 
a good proportion generally. The lac is first melted, and the corundum, after it 
has been reduced to a powder, mixed intimately with it ; the composition is then 
moulded in the shape of a brick (about 6 x 4 X 1§ inch) with a handle of wood, 
about six inches long at one end, having a rise of about 30 degrees, for the con- 
venience of working it. 
The method of preparing the peroxide of tin, may be found in Dr. Henry’s 
Chemistry, vol. II. page 135. 
Having thus given a detail of the introduction of the Jaisalmir stone, I should be 
wanting in candor were I not to explain, that I lay no claim to the original discovery 
of the material ; that credit is due to an officer of Engineers 2 who sent it to Calcutta, 
with many others, to be experimented upon. I am satisfied with being the first 
individual who has brought into use a substitute for the German stone” a point 
long aimed at in Europe, and where, at this moment, they are engaged in attempting 
to make artificial cements to answer the same purpose. 
From numerous specimens of stones which, from time to time, have been sent to 
me for experiment, I have little doubt that a stone possessed of qualities similar to 
the German, will ultimately be found in the lias formation of Bundelkhund, or on 
the Sylhet frontier ; perhaps also in Tenasserim. 
A stone from the neighbourhood of Masulipatam, transmitted by the Private Secre- 
tary to the Governor General, is possessed of lithographic properties, and tolerable 
impressions have been produced from it ; but as the magnesia in its composition is 
in excess, it is difficult to keep a clean surface, or to prevent shading while 
printing from it. I should esteem ita favor, if someof your scientific readers, residing 
in the provinces, would take the trouble to examine the quarries in their neighbour- 
hood, and procure, for the purpose of experiment, specimens (about 6 inches square, 
by 1§ thick,) of stones, having any resemblance to the true lithographic ma- 
terial: the lighter colored, the better. Sand-stones, or marbles, would not be service- 
results' 1 ' reSearCheS “ the limestone formation, would probably lead to successful 
* R S. 
2 Lieut. J. T. Boileau, Executive Engineer, Agra. 
