352 ORGANIC CHEMISTRY. 



8$4. PREVENTIVES OF DECAY. The ten- 



How may the 



decay of wood dency of wood to decay is checked by 



be prevented? ^ and ^ Q b certain salts> p or 



this purpose, corrosive sublimate and chloride of 

 zinc have been chiefly used. The process of impreg- 

 nation with metallic salts is called kyanizing. 



885. INCOMBUSTIBLE CLOTH. Cotton 



How is cloth IT- T ^ i 



rendered in- cloth immersed in a solution or phosphate 

 combustible? Q f ma g nesia j s thereby rendered incombus- 

 tible. Silicate of potassa is also used on wood for the 

 same purpose. 



886. EFFECT OF SULPHURIC ACID ON 



What is the 



effect of sul- WOOD. Sulphuric acid chars or blackens 

 P wood? aCid n wood b y abstracting a portion of the 

 dxygen and hydrogen which it contains. 

 The carbon is then left in excess, with its characteris- 

 tic color. This action of sulphuric acid is a conse- 

 quence of its strong affinity for water, the elements 

 of which it appropriates from most organic substances. 

 Dilute sulphuric acid has another remarkable effect, to 

 be hereafter mentioned. 



887. EFFECT OF NITRIC ACID. Nitric 



What is the -11,, 



effect of nitric ac id gradually consumes wood and other 

 add on wood? organic matter> as effectually as if they 



were burned by fire. The final products of its action 

 are also the same as those of ordinary combustion. 

 This action is accompanied with the evolution of orange 

 fumes, as when the same acid acts on metals. The 

 first effect of nitric acid is to stain wood yellow ; for 

 which purpose it is sometimes employed. Nitric acid 

 may also be made to combine with woody fibre, form- 

 ing gun cotton. 



