CHEMICALS 347 



I. CHEMICALS USED IN PRESERVATION. 



A. PRESERVING FLUIDS : Formalin, alcohol, formol- 



alcohol. 



B. FIXING FLUIDS : Corrosive sublimate, picric 



acid, picro-formol, chromic acid, Flemming's 

 solution, Hermann's solution, osmic acid. 



C. ANAESTHETICS : Cocaine, menthol, alcohol. 



A. PRESERVING FLUIDS. 



Formalin (Formaldehyde, Formol). Formalin and 

 formol are commercial names given to a solution of 

 formaldehyde, which is a gaseous compound, HCOH, 

 in water. This solution, when first placed on the 

 market, contained 40 per cent, of formaldehyde, but 

 it was found that at this strength the solution was 

 liable to undergo chemical changes and to throw down 

 a precipitate, whereas a weaker solution remained un- 

 changed. The solutions of formaldehyde now vary 

 from 30 per cent, to about 40 per cent. Formalin is a 

 powerful antiseptic, and is manufactured on a large 

 scale for disinfecting purposes ; even a very weak 

 solution has a deadly effect upon bacteria. It can be 

 obtained from retail chemists and photographic dealers, 

 but when large quantities are required it is advisable 

 to purchase it directly from a manufacturing chemist, 

 and at the same time to ascertain the strength of the 

 solution. Formalin requires careful handling ; its 

 vapour has an irritating effect upon the nose and eyes, 

 but, fortunately, the irritation soon passes away with- 

 out doing any harm. The action of the solution upon 

 the hands is to harden the skin and to make it slightly 

 rough. Weak solutions, as a rule, are not injurious, 



