44 BULLETIN 1298, U. S. DEPARTMENT OF AGRICULTURE 
REQUIREMENTS A PRESERVATIVE MUST MEET TO BE SUITABLE 
In the selection of a preservative, several characteristics besides 
effectiveness as an antiseptic must be given consideration, such as: 
1. Poisonous properties. 
2. Chemical discoloration produced in the pulp. 
3. Odor. 
4. Solubility in cold water. 
5. In the case of oils, ease of emulsification. 
6. Cheapness and availability. 
Some substances which are quite efficient as antiseptics must nec- 
essarily be ruled out of commercial use, because in the handling of 
either the solutions or the sprayed pulp sufficient quantities of the 
poison might be absorbed through the skin to impair the health of 
the worker. Likewise, violent poisons which might accidentally 
enter the body through- the mouth must be avoided in order to protect 
the consumer. Examples of such dangerous substances are mercuric 
chloride (corrosive sublimate), sodium arsenate, and sodium cyanide. 
Some highly efficient antiseptics produce objectionable discolora- 
tions in the treated pulp, which are due either to the color of the 
chemical or to caustic or other action on the wood fiber. All of the 
alkalies produce browning, the depth of which depends on the sub- 
stance used and the concentration of the solution employed. For 
instance, borax produces a slight browning which is not objectionable, 
whereas both sodium carbonate and sodium bicarbonate will so dis- 
tinctly darken the pulp as to make it unfit for commercial use unless 
it is to be bleached later. Sodium dichromate, likewise, ultimately 
browns the pulp to a considerable degree if applied at a rate of 20 
pounds or more per ton. At some mills there might be objection to 
this darkening, but at the mill where the tests were made there 
seemed to be no objection to it. Sodium dinitrophenolate is appar- 
ently not adapted to commercial use on ground wood in amounts 
larger than 2 pounds per ton. Even at 0.9 pound per ton the yellow 
tint produced, though it readily leaves the pulp on washing, is dis- 
tinctly noticeable. 
None of the substances recommended hereafter give rise to objec- 
tionable odors, but the opposite is true of some of the chemicals 
experimented with. 
Solubility in cold water is a very important property, as in most 
cases the chemicals are most easily applied in the form of water 
solutions. 
Oils are preferably to be emulsified in order to secure the proper 
dilution. The readiness with which they emulsify is an important 
factor in their application. 
Of course, price and availability will have much to do with the 
selection of the chemical to use. The results from the treatment 
must justify the cost of it. How much the treatment will cost 
depends largely on how much of the chemical is necessary to treat a 
unit of pulp effectively. 
CHEMICALS GIVING MOST FAVORABLE RESULTS 
Of the chemicals tried, six gave favorable results in preventing 
mold and decay and also met other requirements sufficiently well to 
warrant their commercial consideration. Brief information concern- 
ing these follows. 
