4A. REPORT—1863. 
The salt presents many features by which its purity can be ascertained. 
1. Its striking peculiarity of form, its complete dryness, and greater specific gra- 
vity than crystals of soda. 
2. It cannot be adulterated with the cheaper salts, sulphate and ordinary car- 
bonate of soda, which contain much water, and fall into powder. 
3. It is the only ordinary salt that can be heated red hot on a piece of charcoal 
without change of crystalline form. It merely becomes opake, while sulphate and 
carbonate of soda undergo watery fusion, common salt decrepitates, and nitrate of 
soda deflagrates. The least-instructed purchasers cannot be deceived as to its 
urity. 
The surface with difficulty effloresces even in an atmosphere so dry as to turn in 
the same time a large crystal of soda into powder. As it contains only 17 per cent. 
of water, and 83 per cent. of carbonate of soda, the cost of distant carriage 1s nearly 
the same as that of ordinary soda-ash of 85 per cent. 
The preparation is more economical than that of the two ordinary forms of soda, 
being produced by the “ multiple ” employment of heat ; and it can be packed from 
the evaporating-pan without deetiche more than a moment. M. Kessler considers 
that all these properties point it out both for the public and the manufacturer as 
the most rational commercial form of soda. 
On Glass-engraving by Hydrofluoric Acid. By M. L. Kesstrr. 
The two principal glass-works in France, St. Louis and Baccarat, have used for 
five or six years M. Kessler's process for engraving on glass by means of hydro- 
fluoric acid, of which various specimens, especially lamp-globes, may be seen any- 
wherein London. The results have been obtained with great economy by printing 
on paper the “‘ réserve” or ground of the pattern with bitume de Judée dissolved in 
essence of turpentine ; the printing is then transferred to the glass, which is plunged 
into a bath of hydrofluoric acid, in which a continual rotatory motion is given to it, 
The glass is acted on wherever there is no printing. When the engraving is suf- 
ficiently deep, the pieces are washed in an alkaline lye, which dissolves the reserve. 
This process has rapidly extended, and has already in great part displaced the 
ancient method of glass-cutting. In view of its increased consumption for this 
_purpose, M. Kessler has simplified the manufacture of hydrofluoric acid, which he 
pt ares in cast-iron cylinders. Asacure for the painful burns caused by this acid, 
e has found a certain antidote in binding on the wound strips steeped in acetate 
of ammonia. 
On a New System of Evaporating Liquids. By M. L. Kesster. 
There is at present an important gap in the list of apparatus for evaporating 
liquids. There are simple evaporators of various kinds, and there are arrange- 
ments in which the heat of the vapour from one liquid boils another more volatile 
liquid. There are also apparatus where the same eflects are obtained by means of 
decreasing pressures corresponding to diminishing boiling-points, but not for the 
multiple so, of the same liquid without the intervention of decreasing 
pressures. is arises from the difficulty of condensing a vapour disengaged in the 
atmosphere, and necessarily of inappreciable tension, and especially mixed with air. 
M. Kessler thinks that for resolving the question the first condition is the placing 
of the vessels above each other, so that the bottom of one shall be the cover of the 
other, as in this arrangement the air charged with vapour will easily ascend to be 
cooled in contact with the cover, then coming into contact with the liquid to be 
saturated with vapour it becomes the agent of its own transport. Constantly in 
motion, it cannot accumulate in the places for condensation and thus prevent the 
vapour from reaching these. 
econdly, to prevent the drops condensed from falling into the liquid below, he 
ives an inclination to the surface of the cover towards the sides all round. The 
rops adhering to the cover by capillary attraction drain into a trough round the 
outer edge of the lower vessel, and are thus delivered outside the apparatus. This 
trough also forms a water-lute between the two vessels. 
M. Kessler says that such an apparatus performs the two separate operations of 
