1815. Scientific Intelligence. 235 
VII. Farther Queries respecting Gas Lights. 
(To Dr. Thomson.) 
DEAR SIR, 
Yours and Mr. Accum’s reply to my queries respecting the method 
of producing illumination by gas, instead of lamps or candles, are 
very satisfactory. I possess his new treatise on the subject; but f 
do not find any directions for choosing pipes of a diameter suitable 
to produce a given effect. He gives no rule concerning the diame- 
ters ; nor does he give sufficient directions concerning the lime used 
for purifying the gas. I hope he will be so obliging as to supply 
these deficiencies through the medium of your Annals, stating at 
the same time the places where pipes, &c. may be purchased on the 
terms mentioned in his book. Mr. Accum being a chemist, L con- 
clude he does not supply apparatus of this magnitude. Is it Mr. A.’s 
opinion that lighting a private house in the country by coal gas 
‘would be less expensive than by candles or oil ? 
Your: obliged, 
July 17, 1815. A. M———«. 
IX. Crystals of Arragonite. 
It is well known that the crystalline form of the arragonite is 
different from that of calcareous spar. M. Stromeyer, after disco- 
vering the presence of carbonate of strontian in that mineral, con- 
ceived that the arragonite derived its crystalline forms from car- 
bonate of strontian. But as carbonate of strontian had never been 
found in regular crystals, that conjecture could not be verified. 
Gehlen has lately announced that he and Professor Fuchs observed, 
among specimens of barytes from Salzburgh, crystals of carbonate 
of strontian having exactly the same form as those of arragonite 
(Schweigger’s Journal, xi. 392) ; so that there seems to be no doubt 
that the crystalline figures of carbonate of strontian and of arra- 
gonite are the same. But this coincidence of form does not appear 
to me to clear up the difficulty. ‘That one part of carbonate of 
strontian should oblige 50 or 100 parts of carbonate of lime to 
assume its own form of crystal appears quite inexplicable. If the 
shape of the crystal depends upon that of the integrant particles of 
the crystallizing body, the crystallization should either be confused 
when two different sets of integrant particles crystallize together, or 
they must combine and form a new integrant particle: 99 parts of 
carbonate of lime mixed with one part of carbonate of strontian 
ought, one should think, to assume the crystalline form of car- 
bonate of lime. The gres des Fontainblois, which has been consi- 
dered as similar, is not even analogous. In it we have crystals of 
calcareous spar mixed with grains of sand; but in the present case 
both bodies must have been in a liquid state, and both are capable 
of crystallizing. 
