6 BULLETIN 145, U. S. DEPARTMENT OE AGRICULTURE. 



The test pieces were then submerged in a glass jar containing 300 

 c. c. of distilled water at room temperature. This water was changed 

 at stated intervals and analyzed for the presence of preservative. 

 The total time of leaching was 4 weeks. To check the amount of pre- 

 servative remaining in the wood after the total submersion period the 

 specimens were shredded and chemically analyzed. Owing to the 

 large amount of preservative which adhered to the surface of the wood, 

 and the absorption of some of it, it was extremely difficult to secure 

 satisfactory results on leaching. For this reason no values are given. 

 Recent experiments indicate that not only do the different salts 

 leach at different rates, but also various concentrations of the same 

 salt. 



INFLAMMABILITY TESTS. 



The crib and shaving tests frequenth T used in testing the combusti- 

 bility of wood proved unsatisfactory, and a new form of apparatus 

 was finally developed with which more comparable results were 

 obtained. This apparatus (see PL IV) consists of a silica tube, 

 wrapped with nichrome ribbon. An iron tube fitted with a mica 

 sight was cemented below the silica tube. 



The specimen of wood, after being lowered in the silica tube, was 

 heated at a uniform rate by passing 24 amperes of electric current 

 at 110 volts through the nichrome ribbon. Temperature readings 

 were obtained from a thermocouple placed beside the specimen and 

 reading direct from a Hoskins -pyrometer indicator. A pilot light 

 was used to ignite the gases distilled from the wood. Compressed 

 air partially dehydrated by expansion was passed through the appa- 

 ratus, its intensity being indicated by a sensitive liquid manometer. 

 Three untreated test specimens cut from stick 11 (see PL I) were 

 burned as a check against the three treated specimens cut from 

 stick 13. When the preservative was a water-soluble salt, the test 

 specimens were first air-dried and then oven-dried before ignition. 

 When the preservative was an oil, one inflammability test was made 

 within 24 hours after impregnation and another after three months' 

 seasoning in the volatility apparatus, the latter being made on speci- 

 mens cut from stick 12. 1 



TOXICITY TESTS. 



Because of the importance of toxicity tests and the inherent 

 objections to various established methods of testing, three independent 

 methods were followed : 



(1) Petri-dish method, in which the preservative is mixed with a 

 culture medium and inoculated with fungi. 



1 Stick 12 was used for leaching tests in the treatments with water-soluble salts, and for inflammability 

 tesl after 3 months' seasoning in the volatility apparatus in the treatments with oils. 



