173 



onl>- liigh gravity oils which arc appreciably cheaper than creosote are certain oil 

 tar distillates. Emulsions in these f)ils of such solutions as zinc chloride, copper sul- 

 fate, and mercuric chloride, would probably possess a considerable protective value, 

 particularly since the oil tar distillate has been found to possess some protective 

 power in itself. 



The methods which we studied chiefly were those involving precipitation in the 

 wood of a so-called insoluble (i.e., slightly soluble) inorganic compound. There are two 

 main methods for doing this. The first is the method of double treatment and the 

 second involves decomposition of the treating solution by some means after treatment. 



To get satisfactory penetration and distribution of the second solution, in the 

 double treatment methotl, it is necessary to dry the wood fairly well after the first 

 treatment. In practice, we found this a matter of some difficulty, and it is probably 

 not economically feasible on a large scale. The double treatment idea was, therefore, 

 abandoned, excepting for our preliminary experiments. 



A preliminary study of the subject was made by treating small Douglas fir 

 blocks with various inorganic substances, including copper sulfide, arsenic sulfide, 

 antimony sulfide, lead chloride, mercurous nitrate, mercuric sulfide, and metallic 

 selenium. The precipitation of some of the foregoing substances in the wood in\'olved 

 a double treatment. As already noted, this was not thought to be feasil)le on a large 

 scale. Hence, a second series of blocks was treated, using single treatment methods 

 believed to be applicable in commercial jiractice. The treatments were as follows, 

 the dry wood being impregnatetl with the acjueous solutions at ordinary temperatures 

 and 90 pounds pressure: 



1. Chandler's Solitlion. Solution contained 8.5% sodium carbonate (NaoCoj), 

 1.5% sodium bicarbonate (NaHCO:,), less than 1%, copper sulfate (CuSOj-SH-jO). 

 This solutit)n must be used soon after preparation, since it gradu.dK' decomposes 

 until the copper content is less than 0.5%, as CuSOrSHiO. 



A. Impregnation in cold. No after-treatment. 



(Chandler's method.) 



B. Impregnation in cold. Steamed after treatment to precipitate cuprous 



oxide (Cu;0) in the wood. 



2. Sodiiini selenite and sodium hydroxide (Na-iSeOs + NaOH). Solution contained 

 5%, selenium dioxide (SeO.) and 0.5%, free NaOH. Steamed after treatment to pre- 

 cipitate metallic selenium in the wood. 



3. Copper sulfate and sodium Ihiosulfale (CuSOt + Na^SiOi)- Solution contained 

 5% CuS0^-5H:0 (crystalline) and 12%, NaoSoOj-SHcO. Steamed after treatment to 

 precipitate cupric sulfide (CuS) and sulfur (S) in the wood. 



4. Mercurous nitrate (IlgNO,). Solution contained 1% HgN03'2H20. No after 

 treatment. Sea water precipitates calomel (HgCl) in the wood. 



5. Mercuric chloride and sodium Ihiosulfate (IlgCli + Na^SiOi). Solution contained 

 l%o HgCb, 4% Na3203-5H,0, and 2%, Na^CO, (sodium carbonate). Steamed after 

 treatment to precipitate mercuric sulfide (HgS), mercurous oxide (Hg;0) and other 

 decomposition products of this solution. 



The foregoing treatments utilize two ideas. The first of these is the use of solu- 

 tions of metallic salts, which precipitate relatively insoluble metallic compounds on 

 heating. The second is the utilization of the reducing power of the wood in precipi- 

 tating relatively insoluble metallic compounds in the wood. The latter method has 

 not to our knowledge been used prior to the work of this Committee. 



Sodium thiosulfate is useful in making up both types of solutions. An excess of 

 sodium thiosulfate added to a solution of a hea\y metallic salt, such as copper sulfate, 



