48 .  REPORT—1858. 
for an indefinite period in the dark, that the precipitation of calomel begins in about 
fifteen or twenty seconds in full sunshine, and that this precipitate ceases immediately 
the vessel containing the solutions is removed from solar influence, showing that the 
action is not continued in darkness after the chemical change has been partially effected; 
that the action of the actinism is not in this case calalytic. When three tubes of the 
mixed solutions are exposed to pretty uniform light, No. 1 for ten minutes, No. 2 
for twenty minntes, and No. 3 for forty minutes, the results are that the tube that had 
been exposed twenty minutes contained twice the bulk of precipitate of that which 
had been exposed but ten minutes, and the tube with forty minutes’ exposure contained 
twice the bulk of the twenty minutes. If the exposure of the solutions be continued 
several hours, the vessel containing them will be completely filled with a magma of 
the precipitated calomel*. 
From these experiments it is concluded that the mixture of solutions of oxalate of 
ammonia and protochloride of mercury is very sensitive to light; that as this action 
of light is not catalytic, all the precipitate obtained from the solutions may be con- 
sidered as being produced by solar influence alone ; and lastly, that a definite amount 
of precipitate is produced by a definite amount of actinic force; thus proving that 
there are elements of uniformity and certainty in the behaviour of the mixed solutions 
under the influence of light, from which a certain method for estimating the actinic 
force may be formed. 
If extreme delicacy be required in the estimations, the precipitated calomel might 
be collected, washed, and dried; but if this is not desired, narrow graduated tubes 
might be used for exposing the mixed solutions, and the amount of precipitate read 
off after standing a certain time in the dark. 
The author used in these experiments nearly saturated solutions of the two salts, 
but the formation of calomel takes place in solutions far removed from the point of 
saturation ; for if a drop of solution of the protochloride of mercury containing only 
rasy of a grain of that salt be added to 300 grains of a solution of oxalate of ammonia 
and exposed to the light, the calomel is precipitated in a light powder; and this deli~ 
cate reaction may therefore be used as a confirmatory test for the presence of the 
protochloride of mercury. 
It would be interesting to know whether the absorbed actinism of M. Niépce de 
St. Victor would affect the mixed solutions. The author has tried several experiments 
in this direction, but not with sufficient success to warrant any positive assertions, 
On a Method of Observation applied to the study of some Metamorphic Rocks ; 
and on some Molecular Changes exhibited by the action of Acids upon them. 
By Auvuonss Gaczs, Curator of the Museum of Irish Industry, M.R.1.A. 
The author, while admitting that the ordinary method of analysing rocks gives their 
absolute composition, is of opinion that it does not give any information as to their 
genesis or decomposition. ‘The preliminary mechanical operations to which the spe- 
cimens to be analysed are submitted wholly destroy their peculiar state of aggregation, 
and mix up substances that may not have been in combination. He accordingly 
proposes a new method of examination, which is applicable in a great many cases, 
and which is capable of leading to extremely important results in connexion especially 
with metamorphic rocks. His method is to expose fragments or thin laminz cut in 
certain directions, or whole crystals to the action of acids, alkalies, or other solvents 
for a certain time. 
The author gave several examples illustrative of his method, of which the following 
are the most interesting. 
A fibrous dolomite of Miask in the Ural Mountains, analysed by the ordinary me- 
thod, yielded — 
Carbonate OF Te een. oan ans nie ee Os BOD 
As magnesia ........+... 40°974 
Sesquioxide of iron andalumina .,.. 0°411 
Water and organic matter..........  0°239 
Se See hminasda> hme 805 <aihk Sa 
100°202 
%* The mixed solutions may be boiled in darkness without any precipitation of calomel. 
