8 BULLETIN 549, U. S. DEPARTMENT OF AGRICULTURE. 
were also treated a few miscellaneous ties, chiefly cypress, ash, syca- 
more, locust, and hickory. 
Zine chloride was the principal preservative used. Large quanti- 
ties of creosote were also consumed in the treatment of ties. Zine 
chloride and creosote in combination treated 2,182,712 ties, of which 
over 50 per cent were oak. The miscellaneous preservatives were 
used principally for Douglas fir and tamarack. 
In treating ties with zine chloride the average injection of the pre- 
servative was 0.5 pound per cubic foot, while with creosote oil the 
average quantity used was 8.5 pounds per cubic foot. 
The practice of treating wood has increased because of the eco- 
nomic necessity of less frequent renewals of timber subject to decay. 
Prior to 1900 the wood-preserving industry developed slowly, and 
only during the last 10 or 15 years has it gained a permanent foot- 
hold in the United States. From a total of 12 plants in 1900 the 
industry has grown until at the present time there are 128 plants in 
commercial operation. Of this number 95 are pressure plants, 27 
are nonpressure plants, and 6 are equipped for both pressure and 
nonpressure treatment. The industry in this country has been built 
up largely on crossties and other railroad material. Of the total 
quantity of 141,858,963 cubic feet of material of all kinds treated 
with preservatives in 1915, a little more than 78 per cent was crossties. 
The number of ties treated each year, beginning with 1909, is 
shown in Table 9, together with the quantity of ties reported pur- 
chased. 
TaBLE No. 9.—Nuwmber of crossties reported purchased and treated, by years. 
Reported Reported 
Year. purchased. treated. 
1909 | 123,751,000 | 20,693,013 
1910 | 148,231,000 | 26,155,677 
1911 | 135,053,000 | 28,394, 140 
1912 (1) 32, 394, 336 
1913 (1) 40, 260, 416 
1914 1 43, 846, 987 
1915 97,106,651 | 37,085,585 
1 Statistics for these years not obtained. 
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