2 BULLETIN 620, U. S. DEPARTMENT OF. AGRICULTURE. 
base is present. Lime is the base in most common use. For a 
long time it was not known how much of this was necessary to make 
good pulp, most mills simply taking the acid that their systems. 
gave them. Many are still following that practice. Most mills 
have a good idea of how the different factors affect their cooking, 
but there is no published report on the subject. It was to furnish 
detailed information on just how much each of the various factors 
influences the cooking and to supply a basis for future experimental 
work that this investigation was undertaken. 
THE SULPHITE PROCESS. 
The inventor of the sulphite process, Benjamin C. Tilghman, of 
Philadelphia, took out a patent in the year 1867, in which he describes 
a method of boiling under pressure wood or other vegetable material 
in a solution containing sulphurous acid, with or without the addition 
of sulphites, until a fibrous product is obtained suitable for the manu- 
facture of paper. The foundation of the sulphite pulp industry 
rests upon these patents; yet Tilghman had to abandon his process 
because his financial backers withdrew their support upon finding out 
that sulphurous acid corrodes iron and that the inventor was having 
difficulty in obtaining a suitable lining for his digester when he tried 
to work his process on a large scale. 
For some time this difficulty hindered the development of the 
process. In 1886 cement and special brick linings were introduced 
in some mills and gave such good satisfaction from the start that it 
was not long before they were universally adopted. The solution 
of this problem insured the commercial success of the sulphite in- 
dustry, and from this time on it has had a rapid growth, until now 
it is the most important pulp making process in the United States, 
as is shown by the figures in Table 1 taken from the census reports. 
TABLE 1.—Quantity of wood pulp produced in the United States. 
: Value Value 
Process. 1890 1899 1909 (1909). 1916 (1916). 
Tons. Tons. Tons. Tons. 
Pas Ulphite see ear ee eee 59,686 | 417,646 | 1,027,012 |$44, 600,000 | 1,306,217 | $60,702, 459 
Sodaitsisss Ae ee, Sea eee 87,853 | 172,142 287,945 | 12,770, 000 183,106 > 201,219 
Ground wood? serene eee ee 290,158 | 568,284 | 1,201,832 | 25,200,000 | 1,505,547 | 32,547,704 
KINDS OF WOOD USED. 
In the early days spruce was almost the only wood used in making 
sulphite pulp, but it was not long before hemlock and balsam began 
to be used extensively. At the present time some mills are cooking 
tamarack and poplar, and on the west coast white, red, amabilis, and 
grand fir, sitka and Engelmann spruce, western hemlock, and other 
woods are finding favor. No doubt it will not be long before 
