AN IMPROVED PROCESS FOR THE PRODUCTION OF PHOSPHORIC ACID IN THE MANUFACTURE OF GLASS
Year: 1880

page_text: PROVISIONAL SPECIFICATION left by William Robert Lake at the Office
of the Commissioners of Patents on the 6th January 1880. A communi-
cation from abroad by Charles De la Roche, of Paris, France.
WILLIAM ROBERT LAKE, of the Firm of Haseltine, Lake, & Co., Patent Agents,
Southampton Buildings, London. "AN IMPROVED PROCESS FOR THE PRODUCTION
OF PHOSPHORIC ACID IN THE MANUFACTURE OF GLASS." A communication from
abroad by Charles De la Roche, of Paris, France.
The large consumption of phosphoric acid, particularly for agricultural purposes,
has for a long time caused chemists to seek means for obtaining this substance
cheaply. It is found principally in nature, combined with lime, in phosphates of
lime, such as those found in the Department of the Lot, France, in Canada, in
Norway, and in Spain.
Nearly all the processes heretofore employed or suggested are based on the use
of sulphuric acid, which acting on the phosphate of lime absorbs a portion of its
base, and reduces it to the state of an acid phosphate of lime, containing a certain
quantity of assimilable phosphoric acid.
This mode of proceeding has two disadvantages, that is to say, it gives a
relatively small return, taking into consideration the quantity of phosphoric acid
which remains confined in the cakes of phosphate of lime which always retain it
whatever may be the pressure to which the cakes are submitted; and the phosphoric
acid, or rather the acid phosphate obtained, which always carries with it a large
proportion of lime or of sulphate in lime, loses much of the proportion of acid that
can be assimilated, which it contained at the time of manufacture.
Other processes have had for their object the enrichment by successive operations
of the phosphates, abstracting from them the whole or a portion of the gangue that
impoverishes them. This method of producing super-phosphates, although a step
in advance, possesses the disadvantage of requiring the use of acid, which, while
increasing the cost of production, limits the application of the process to richer
phosphates than those forming the average of the rocks or stones obtained from the
mines.

page_text: This composition furnishes transparent glass.
Instead of 90 kilogrammes of lime, I use in the composition a weight of phosphates
containing 90 kilogrammes of lime; thus the glass is furnished with the lime it
requires, and will moreover, during the calcination, throw off a certain quantity of
phosphoric acid which I am able to obtain.
Under these conditions the secondary product I obtain in the crucible will be a
fine toned glass, useful for the manufacture of drinking glasses or tumblers, and able
to compete with the productions of Bohemia.
According to the degree of heat, I can also produce by this process an opal glass
of handsome appearance, and especially serviceable for the manufacture of fine art
glass ware.
The quantity of phosphate used will vary not only in consequence of its com-
position, but also according to the nature of the glass required to be made.
Practically the operation can be effected in ordinary glass furnaces; I place on the
crucible lids a pipe of non-oxidable metal for the escape of the gases; into this pipe
a lead tube is inserted, one end of which is in a receptacle containing water. A
narrow tube placed near the orifice of the crucible allows of the precipitation of the
gases at the beginning of the operation by throwing a small jet of water which is
immediately vaporized.
The crucible being charged, the carbonic acid gas, combined with lime and the
permanent gases, is the first to free itself, but soon also, in the shape of white smoke,
phosphuretted hydrogen and phosphoric acid follow, the latter carried off by silicic
acid of the sand reaches the bottom of the water which becomes acid. The operation
is considered complete when the glass is fine, this requiring from 48 to 57 hours of
fusion. In limiting the period of fusion to about 36 hours, a small quantity of
phosphoric acid remains in the crucibles, it is true; but on the other hand a very
beautiful opalescent glass, having a high commercial value, is obtained. The glass
obtained by this process (although resulting from the employment of proportions
which usually give ordinary glass, for example, bottle glass) is of superior quality
and resembles crystal. The acidulated water obtained is concentrated, either by
evaporation, or by repeated liberations of the gases; the latter method is the

page_text: more economical, and by it are obtained liquids of a gravity of from 45 to 55
Baumé.
I may employ phosphates and produce phosphoric acid, as above set forth, in all
methods of glass manufacture. The cost of production of glass, which is considerably
reduced by the substitution of tale-schist and mica-schist for silica, undergoes
another considerable reduction by the substitution of phosphates of lime for lime,
which substitution results in the direct production of the acid of the phosphate, and
gives an emerald glass of a superior quality.