364 
POPULAR SCIENCE REVIEW. 
takes his prints from the frame and places them in a solution of common 
salt of 5 per cent, strength, leaves them there for some time in the cold, and 
then gradually heats the bath up to boiling-point for about ten minutes, after 
which the print becomes completely “fixed.” — See Chemical News, June 1. 
Crystalline Chromic Acid. — According to the analysis of Rainmelsberg, 
this acid is a true anhydride. The crystals examined by him contained 
sulphuric acid. — Poggendorff's Annalen, No. 3. 
The Nature of Silicates. — In his lecture on Chemical Geology, recently 
delivered in the School of Mines, Dr. Percy entered into considerable details 
regarding the general and chemical characters of the silicates. He gave the 
following account of the physical qualities of these substances : — They are 
all solid and hard, and generally brittle, but varying greatly in this respect, 
some being exceedingly tough and others just as brittle, breaking sometimes 
with a stone-like fracture, sometimes with a conchoidal fracture, like a piece 
of glass, and possessing almost every tint of colour, according to the materials 
which they contain. “We have blue silicates, red silicates, yellow silicates, 
and all kinds of coloured silicates. Here, for example, is a blue silicate. 
It is a silicate of cobalt essentially with alumina and other things. It has a 
fine blue colour. Then there is the red colour. Take, for example, the 
silicate of some oxide of copper. Of this you have a specimen in this stained 
bottle. Here is another specimen having a red colour. This is a very curious 
specimen in other respects, because when viewed by transmitted light the 
colour is green or bluish-green. We might go on multiplying examples, but 
it would be useless on the present occasion. Suffice it to say we have every 
tint. Here, for example, is a silicate of the protoxide of copper, very easily 
made. Here is a silicate which is prepared artificially by double decomposi- 
tion. The various coloured glasses we see owe their colour entirely to silicates 
of metallic oxides.” 
Use of Lime in extracting Sugar. — Peligot long ago demonstrated that 
owing to the insoluble nature of the compound formed of lime with sugar, 
the former substance would be a most valuable agent in the manufacture of 
the latter. Peligot’s suggestion is now being carried out on a large scale in 
MM. Schrotter and Wellman’s sugar-factory at Berlin. The molasses is 
mixed with the requisite quantity of hydrate of lime and alcohol in a large 
vat, and intimately stirred for more than half an hour. The lime compound 
of sugar which separates is then strained off, pressed, and washed with spirit. 
All the alcohol used in the process is afterwards recovered by distillation. 
The mud-like precipitate thus produced is mixed with water and decomposed 
with a current of carbonic acid, which is effected in somewhat less than half 
an hour. The carbonate of lime is removed by filtration, and the clear liquid, 
containing the sugar, evaporated, decolourized with animal charcoal, and 
crystallized in the usual manner. The sugar furnished by this method has a 
very clear appearance, and is'perfectly crystalline. It contains, according to 
polarization analysis, sixty -six per cent, of sugar, twelve per cent, of water, 
the remainder being uncrystallizable organic matter and salts. The yield, of 
course, varies with the richness and degree of concentration of the raw 
material ; on an averagfe, 30 lbs. of sugar were obtained from 100 lbs. of 
molasses. 
Composition of the Waters of the Red Sea , Dead Sea, and Mediterranean . — 
