Phosphorus is stored either in strong sheet-iron tanks or in wooden boxes lined with tinned sheet-iron and covered with a stratum of water fully 1¼ inches deep. For shipping smaller quantities of phosphorus, the sticks are packed in tinned sheet-iron boxes and the latter having been filled up with water, the lid is soldered on. To prevent the water from freezing in winter, it is advisable to mix it with spirits of wine.
Manufacture of phosphorus with the assistance of electricity. Readman and Parker have recently devised a process for the manufacture of phosphorus on a large scale in a continuously working apparatus by means of a powerful electric current, such as is yielded by a larger dynamo. The mixture used for the operation differs from the ordinary one of calcium phosphate and charcoal, in that it contains in addition a slag-forming body—a flux—silicic acid (quartz sand) being at first used for the purpose. Numerous experiments, however, have shown kaolin or pipe clay, i. e., aluminium silicate, to be more suitable.
When a mixture of calcium phosphate, charcoal and aluminium silicate is exposed to the action of the voltaic arc the following process takes place: By the extraordinarily high temperature prevailing in the proximity of the arc, the reduction to phosphorus of the phosphoric acid contained in the calcium phosphate is very rapidly effected. The liberated calcium combines immediately with the aluminium silicate to a calcium-aluminium-silicate, i. e., to a glass fusible with the greatest difficulty which, however, at the high temperature possessed by the voltaic arc becomes fluid like water.
The apparatus employed is, generally speaking, similar to the electric furnaces now in use. The mass to be treated is contained in a carbon crucible in which the two electrodes are placed opposite to one another, so that the electric current must pass through the mass. However, since the phosphorus at the moment of liberation would, on coming in contact with oxygen, immediately burn again to phosphorus pentoxide, the apparatus has to be so arranged that the entire process passes off in an entirely indifferent gas, and the condensation of the phosphorus vapors takes place under the same conditions.
Fig. 56 shows the apparatus employed for the electrolytic manufacture of phosphorus.
Fig. 56.
The carbon crucible, a, is enclosed by a clay jacket, which serves as an insulator of heat, and is closed by a graphite cover, c. Through the bottom and the cover of the crucible pass the two electrodes, k k, which conduct the current, and between which the voltaic arc is formed. To prevent the upper electrode from becoming too highly heated during the operation, it is constantly cooled by water admitted at g, and running off at f. Through the pipes h and l an indifferent gas—as a rule, illuminating gas—is conducted into the apparatus and escapes together with the phosphorus vapors through the pipe d.
In operating with the apparatus, the reduction soon takes place, and the phosphorus vapors escape through d, while a thinly-fluid slag remains behind in the crucible. The slag is discharged through a pipe not shown in the illustration, and a fresh charge of the mixture brought into the crucible a, the process of reduction being thus carried on without interruption. The phosphorus vapors escaping from d are conducted through a cooled pipe and condense to a liquid in water heated to between 122° and 140° F. contained in a receiver.
Although the electrolytic method of manufacturing phosphorus is of quite recent origin, a considerable portion of the phosphorus brought into commerce is now prepared in that manner, it being cheaper than the older processes which involve a very large consumption of fuel.