Scientific Notes. 
1877-] 
285 
oreign metals of the platinum group, except ruthenium, which is only in 
traces found in these ores. He also gives analyses of some newly found 
platinum-ores near these districts, which may be of some interest to chemists 
studying the properties oi the compounds of rare metals of the platinum group 
as the ore is sold at the Mint in St. Petersburg at a very moderate price. 
Microscopy. — The oxyhydrogen microscope has been greatly improved by 
Mr. John Browning. Those who are familiar with the old instrument will 
notice a great increase of defining power, and when a suitable surface is 
employed to receive the image, some of the coarser diatoms, such as Aracli- 
noidiscus and Isthmia are not only fairly shown, but will bear being viewed with 
some amount of additional magnifying power. Great care has been taken in 
the arrangement of the condenser to prevent the object from being injured by 
the intense heat of the lime-light, and, with such success, that balsam-mounted 
slides can be Used with safety. The object-holder is adapted to receive the 
ordinary 3x1 slide. This instrument will prove a great desideratum for 
lecture room and class demonstration, and for this purpose, when the objedt is 
not too opaque or of an unfavourable colour, and tolerably flat, it will be found 
all that could be wished. It works well upon a disc of from 4 to 5 feet 
in diameter.* Microscopists must not expect even of this improved instru- 
ment the resolving or defining power they have been accustomed to 
with their usual microscopes; the conditions are entirely different, and 
involve many construdlive difficulties, and the lime-light is, after all, a 
feeble source of illumination where great magnifying power is required. 
The instrument is rather to be judged in comparison with the older forms of 
gas microscope, and, when so examined, will be found a great improvement on 
all its predecesrors. 
The President of the Royal Microscopical Society, H. C. Sorby, Esq., 
F.R.S., in his Anniversary Address laid before the Society his observations 
on the strudture of disintegrated rocks, such as occur in various sands, clays, 
&c. He was led to investigate the subjedt chiefly by having undertaken to 
examine and describe the mineral constituents of the deep ocean deposits 
brought back by the “Challenger.” For the results of these researches our 
readers must be referred to the original paper f as the subjedt cannot well be 
abridged ; as, however, the processes employed in investigation may aid other 
observers, they are given at some length. When stratified rocks are 
sufficiently hard and consolidated to be made into thin and partially trans- 
parent sections, many fadts may be better seen in slices cut perpendicular to 
the stratification than by attempting to disintegrate the rock and examine the 
detached particles. It would, however, often be difficult to prepare thin 
sedtions of many deposits, and it becomes necessary to study them in another 
manner. If the particles are firmly held together by calcic or ferrous 
carbonate, or by any of the oxides of iron, they may be set free by the adtion 
of cold dilute hydrochloric acid, or by a stronger hot solution : but if the rock 
is consolidated by means of silex, this cannot be accomplished. Violent 
mechanical crushing must be avoided, since it would give rise to false results 
by fradturing the constituent grains. Such an amount of crushing as can be 
effected with a small stiff brush made with bristles does, however, appear to be 
admissible, since it could scarcely break the separate fragments. A portion 
of the crushed material may then be sufficiently diluted with more water, 
placed on a glass slip with a projecting ledge, and covered with a piece of the 
usual thin glass. By this means the larger particles are seen separate, butthe 
smaller have a great tendency to mass themselves together. Since the index 
of refraction of the various grains is in all cases considerably greater than 
water, the outline of even the most transparent constituents is well seen, but at 
the same time this difference in refractive power may make it impossible to 
study the internal structure or optical characters of the larger grains. This 
difficulty is overcome by mounting in Canada balsam, which has so nearly the 
same index of refraction as that of many of the constituent grains that, even when 
* With a powerful eleftric light a disc of 7 or 8 feet diameter can be obtained. 
f Monthly Microscopical Journal, vol. xvii., p. 1x3, March, 1877. 
