Alkali Processes.—The first to develop the alkali process {66} were Watt and Burgess, in America (1853–1857), and Houghton in this country. To follow up the several modifications introduced is unnecessary; they differ from one another in the economical balance which they strike between temperature and quantity of chemicals: thus Watt and Burgess employed a lye of 12° Baumé, and digested at 60 lb. pressure (equal to 152° C.), whereas Houghton used a lye of 4° B., at 100–180 lb. One great defect of these processes was the gradual neutralisation of the alkali, necessitating as a compensating condition the employment of a very high temperature towards the end of the operation. To overcome this objection, Ungerer devised a process which aimed at securing a properly graduated action of the lye. This process, being based on an eminently rational view of the action of the alkali, is worthy of a more extended notice, especially as the principle on which it is founded is capable of wide application. A system of nine vertical digesters, connected together in series by means of pipes and cocks, so that the liquid contents can be transferred from one to the other in succession, is the main feature of the method employed. In connection with this system there is a double service of pipes, by which the hot soda lye at 90 lb. pressure, and cold water, may be respectively introduced. The operation is so conducted that in five of the digesters wood is being treated at a high temperature, in three the pulp is being washed, while the remaining one is being charged with fresh wood. The whole round of operations may be described thus, numbering the digesters according to their position in the series:—Nos. 1, 2, and 3, Washing the finished pulp; 4, Final treatment with lye at the extreme pressure of 90 lb.; 5, Digesting at lower pressure with lye previously employed in 4; 6, Treatment at still lower pressure with lye which has already done duty in 4 and 5; and so on to 8, where the liquor, having passed through the series, is employed at 15–20 lb. pressure on a fresh charge of wood. The washings are conducted in such a way that the water which is introduced into 1 displaces the solution in each digester without {67} the last being allowed to escape. The introduction of the fresh liquor at 4 is similarly accomplished, 1, 2, and 3 being cut off by closing the cocks which control the ingress and egress of liquid. The pulp produced by this method is of a sufficiently pale colour to be capable of application for many purposes without bleaching. It is converted into a perfectly white pulp by treatment in the ordinary way with from 3 to 4 per cent. of bleaching powder, calculated in the dry pulp. As far as it goes the method is practically perfect, and it appears to have given sound results, at least as regards the main product. The principal disadvantages were the complications attending such an elaborate system of working which would doubtless make it costly.