94 
POPULAR SCIENCE REVIEW. 
How to Silver Glass. — Those who are familiar with Baron Liehig’s inves- 
tigations on the subject of glass silvering are aware of the numerous diffi- 
culties that attend the deposition of mercury amalgam upon glass ; the follow- 
ing method which has been suggested by Herr Bernhardt will interest our 
chemical readers. Prepare four solutions — first, 10 grammes of nitrate of 
silver to 100 grammes of water ; second, an aqueous solution of ammonia of 
0-984 density; third, 20 grammes of caustic soda and 500 grammes of 
water ; and fourth, a solution of 25 grammes of sugar in 200 grammes of 
water, to which is added a cubic centimetre of nitiic acid, at 36°, and let the 
whole boil for twenty minutes. When cold, add 50 cubic centimetres of 
alcohol, and as much water as will make up the total quantity to 500 cubic 
centimetres ; then take 12 parts of the first, 8 parts of the second, and 20 
parts of the third solution, add 60 parts of water, and let the mixture 
stand for twenty-four hours ; lastly, the solution No. 4 is added when the 
whole becomes of a blackish tint, in consequence of the finely divided pre- 
cipitate of silver which begins to fall. M. Bernhardt has discovered that 
the deposition of the silver is greatly aided by motion, and that, when the 
bath is continually shaken, the deposit on the inner surface of glass vases is 
always satisfactory, and he recommends that in silvering plates of glass they 
shall be placed in evaporating dishes, or other vessels, so that the sides may 
give an oscillating motion to the liquid in the bath when shaken. In acting- 
on large articles, he recommends the glass plates, or other objects, to be 
fixed within tubs or vats, which may then be rolled or rotated pretty 
rapidly. — Journal of Society of Arts, November 1866. 
Observation on the Passage of the Spark of an Induction - Coil through Flame. 
By A. Kundt.— If the current of sparks of an induction-coil be passed 
through the luminous flame of gas or of a candle, no alteration is seen in 
the flame, excepting that in the path of the sparks the flame is intensely 
luminous, and under certain circumstances this brightly luminous path 
of sparks is traversed by dark cross bands. When the polar wires are suitably 
introduced, it appears constant and steady. Yet, if the flame is viewed in 
a slowly rotating mirror, or in one which is moved to and fro in the hand, 
this apparent constancy is found really not to exist ; for, looked at in the 
mirror, the image does not seem constantly broadened, but the part above 
the spark appears alternating, like the flame of a chemical harmonicon when 
looked at in a rotating mirror. From the upper point of the flame to the 
spark, the image in the mirror appears to have serrate incisions, and at the 
lower point of each dark incision there is a passing spark. During this 
transition of an individual spark, the flame, therefore, is always extinguished 
above. The part below the spark is constant and steady. 
On the Deportment of Solutions of Glauber's Salt on Reduction of Tempera- 
ture. — As the physical processes in the so-called supersaturation of Glaubers 
salt solutions have as yet found no sufficient explanation either from physi- 
cists or chemists, it will not be uninteresting to our readers if we place be- 
fore them the conclusions of Dr. F. Lindig, of Schwerin. 
If a solution of Glauber’s salt, whether saturated or not, is allowed to 
cool slowly, it contracts with diminution of temperature, like any other 
body, as long as there is no crystallisation. But as soon as the first crystals 
form in the clear solution, instead of contracting, it begins to expand, and 
