PROTECTING WOODS AGAINST TERMITES. 13 



Timber impregnated with sodium fluorid is apparently as resistant 

 to attack by termites as timber impregnated with zinc chlorid (stand- 

 ard specification one-half pound of dry salt per cubic foot) . Sodium 

 fluorid, however, is much more expensive than zinc chlorid. 



Another method is the " Kyanizing " process, consisting of a steep- 

 ing treatment with a 1 per cent solution of bichlorid of mercury; 

 this chemical, however, is extremely poisonous (see p. 15), which 

 may greatly restrict its use. All of the above treatments are effective 

 for flooring, interior woodwork, other fixtures, or furniture. 



Impregnation with chlorinated naphthalene is an effective treat- 

 ment for valuable cabinet woods or expensive furniture; it is also 

 a moisture-retarding treatment. 



Chlorinated naphthalene is a crystalline wax with a melting point 

 of. about 196° F. It is made in several grades varying in specific 

 gravity, melting point, and other characteristics, according to the 

 extent to which the chlorination process is carried. 



The chlorinated naphthalene used in these tests is a mixture of 

 various chlorinations as well as free naphthalene, with a large pre- 

 ponderance, however, of tri chlor naphthalene. 



This material is usually referred to as tri chlor naphthalene and, 

 as compared with other chemicals, it is really comparable to a 

 technical product having naphthalene, mono chloro naphthalene, 

 di chlor naphthalene, and probably some of the higher chlorinations 

 as impurities. Its melting point ranges between 190° and 210° F. 

 This is the specification under which it is sold. 



The grade used in these tests, as identified by the melting point 

 stated, sells at 36 cents per pound in carload lots ; a less refined grade 

 can be purchased for 20 cents per pound in the same quantity. 



The samples of wood for test were treated as follows: Blocks of 

 the wood 6 by 6 inches by ^ inch were placed, without previous dry- 

 ing, in an open pot of the chlorinated naphthalene at a temperature of 

 from 220° to 240° F. and allowed to remain fully covered by the 

 molten wax for 15 minutes. The blocks of wood were then removed 

 and wiped off with a cloth. The treated wood can be stained, shel- 

 lacked, and varnished. The resultant color will be somewhat darker 

 than the color of untreated wood, and care must be exercised in 

 cleaning the surface thoroughly to insure proper adherence of shellac 

 or varnish. 



The different woods varied greatly in the amount of wax taken 

 up in the above treatment. Furthermore, the amount of wax taken 

 up will vary according to the size and condition of the wood treated. 

 The blocks carried approximately 5 per cent of wax, or at the rate of 

 from 2 to 3 ounces of wax per board foot. At the above price for 

 the impregnating material, the treatment would be rather expensive 

 and possibly prohibitive for ordinary use, such as flooring. 



The treatment also renders the wood moisture-retarding to a 

 marked degree, and its cost is sometimes justified by this double 

 effect. • 



In the tests of untreated woods and woods that were treated with 

 preservatives for use in finished forest products, such as furniture, 

 cabinets, etc., experimental blocks of wood from various species of 

 both coniferous and broad-leaved trees were buried in the ground 

 with logs heavily infested with termites (Reticulitermes spp.) at 

 Falls Church, Va. These blocks were 6 inches square by one-half 



