TIN AFFORDS A GOOD TEST FOR PLATINUM. 
8. Mr. JOHNSTON MADE SOME OB- 
SERVATIONS ON THE OPTICAL 
PROPERTIES OF CHABASITE, IN 
REFERENCE TO THOSE MADE BY 
SIR DAVID BREWSTER AT LAST 
MEETING. 
Sir David found that this mineral possess- 
es different refracting powers at different 
depths of the crystal, and he concluded, that 
it consisted of distinct layers, and that if 
subjected to experiment it would afford the 
result of a compound substance. His results 
refer to particular species only ; but the 
composition of the species vary, and are as 
represented here 
NjU -F 3 A S2 + 6 Aq. 
where Mr. J. conceives that it is easy to see 
the cause of the difference, for the refractive 
power of chabasite is positive, and that of 
quartz negative ; thus accounting for the 
double refracting power observed by Brews- 
ter. 
Dr. Thomson remarked that the observa- 
tions of Brewster probably referred to one 
species of chabasite. But there are two 
species, the one containing soda and the 
other lime as a base. He, therefore, con- 
sidei'ed that until both species were ex- 
amined, no inference whatever could be 
drawn. 
9. Dr. DAUBENY STATED, THAT AC- 
CORDING TO THE OPINION OF 
VON BUCH, CARBONATE OF MAG- 
NESIA MUST HAVE BEEN SUB- 
LIMED IN MANY INSTANCES BY 
VOLCANIC ACTION, ALTHOUGH AS 
FAR AS Dr. DAUBENY WAS AWARE, 
IT WAS NOT AGREEABLE TO THE 
RESULTS OF CHEMISTS. 
A curious fact illustrative of the truth of 
Von Buch’s opinion, occurred to Dr, Daube- 
ny in Italy. He visited. a locality where 
there was an upper stratum of lava, con- 
taining cavities. In one of these Colonel 
Robinson discovered a large quantity of car- 
bonate of magnesia. Dr. Daubeny found a 
quantity coating the upper surface of the 
lava. 
Dr. Dalton observed that there could be 
no doubt as to the sublimation of carbonate 
of magnesia, as Dr. Henry had informed 
him that a quantity of this salt was always 
driven off whenever the heat was carried 
beyond a certain height. 
19. Dr. DALTON STATED THE RE- 
SULTS OF HIS EXAMINATION OF 
THE SPIRIT DISTILLED FROM 
CAOUTCHOUC. 
He found it to depress the barometer like 
sulphuric ether. It passes through water 
without diminishing its volume, thus differ- 
ing from ether. It is absorbed by water 
like olefiant gas. It consists of 2 olefiant 
gas. 10 vols. when burned give 40 carbonic 
acid, and require 60 of oxygen. It appears 
to be the same as a substance described by 
Faraday. It differs from coal gas in this, 
that the latter consists of double olefiant gas. 
The observations of Mr. Davy upon this 
subjecL corresponded with those of Dr. Dal- 
ton. 
Wednesday, August I2th. 
11. Mr. J. MALLET DESCRIBED 
THE PHENOMENA PRESENTED IN 
LAMPS, 
When the holes for the passage of 
the gas are made as small as possible, 
and also the appearance observed when 
the direction of the tube is inclined in differ- 
ent ways, two currents being formed when 
the tube is inclined, and the surface of the 
flame presenting spiral lines, and considera- 
ble retraction of the flame taking place, none, 
however, occurring when the tube is not 
fully inserted. The apertures in the lamp 
were less than the , Jg of an inch in diameter. 
In the discussion wLich arose from this 
communication. Dr. Dalton observed, that 
12 small holes in a lamp consumed less gas 
and gave more heat than when the holes ^ere 
larger but fewer in number. But the great 
object in procuring a proper quantity of heat 
depends upon the atmospheric air being 
neither too great nor small in quantity. He 
stated, that if we. take a cubic inch of pure 
gas, and another diluted with half its volume 
of .air, each gives out the same quantity of 
heat, but the latter scarcely yields any light. 
This is an important fact, and deserves to be 
known. 
12. Mr. CONNELL READ A PAPER IN 
WHICH IT WAS HIS OBJECT TO 
POINT OUT SOME CHEMICAL FACTS, 
By which we may be enabled to detect, 
whether a fossil scale be that of a fish, or 
sauroid animal, and illustrated his position 
by some analyses which he had made on re- 
eent crocodile and fish scales, and upon the 
scales found at Burdie House. His inference 
was, that chemical analysis completely veri- 
fied the idea of Agassiz, that the scales found 
at Burdie House were those of fish. He 
considers the animal matter to be replaced 
by a little carbonate of lime and silica. 
13. Mr. KANE DESCRIBED TWO 
COMPOUNDS OF TIN AND PLATI- 
NUM FORMED BY THE ACTION OF 
PROTOCHLORIDE OF TIN UPON A 
SOLUTION OF PLATINUM. 
One of these compounds consists of an 
atom of each chloride. It deliquesces in the 
air ; is a dark solid substance when anhy- 
drous, and when allowed to remain in the 
air is converted into an olive liquor, which 
is resolved into the oxides by the action of 
water. The author suggested that tin affords 
a good test for platinum. 
