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BELL SYSTEM TECHNICAL JOURNAL 



in the agar is not so easily accomplished. Many salts may be made soluble 

 by dissolving them in dilute ammonia or acetic acid solutions. For example, 

 copper arsenate or zinc m.eta-arsenite are soluble in ammonia or acetic acid, 

 and by evaporation of the volatile portions of the solvent the salts are pre- 

 cipitated. When precipitation of the salts from ammoniacal or acetic acid 

 solution is carried out in treatments of wood, subsequent evaporation of 

 ammonia or acetic acid from the wood is rather rapid. In agar solutions, 

 uniform precipitation of the salts through evaporation of the ammonia and 

 acetic acid is not easily attained. 



Table 3 

 Twenty Four Week Soil Assay of Wood Preservative Compounds Not Readily 



Ass AY ABLE BY PETRI DiSH METHODS 



* Average per cent weight loss of untreated blocks in the same bottles with the treated 

 blocks. 



Agar cannot readily be used for assa}-s of two other types of compounds 

 used as wood preservatives. The first type depends on chemical reactions 

 with and also within the wood. Specific examples of this t}-pe are the series 

 of compounds fi.xed in the wood by the reduction of chromium salts which was 

 first studied by Kamesam,^' 1934. It is now the generally accepted view 

 that the reduction of the chromium is brought about by various sugars in 

 the wood. Subsequent research led to the use of Ascu (Kamesam) or Green- 

 salt K and to the later development of Greensalt "0" by the Bell Telephone 

 Laboratories in the United States and the Bolidens' salts in Sweden. These 

 inorganic salt mixtures were developed in the search for preservatives which 



