FORMALIN 351 



for many years as 40 per cent, strength, and partly 

 because it is very easy to read percentages in a centi- 

 metre measure. 



Successful preservation with formalin depends upon 

 using sufficient formaldehyde to fix every cell in the 

 specimen, and a surplus sufficient to prevent subse- 

 quent maceration. A specimen which is properly 

 fixed and preserved in 50 ex. of formaldehyde 4 per 

 cent, can also be fixed and preserved in 50 c.c. of 

 formaldehyde 2 per cent., providing that the latter 

 solution be changed once. It is much the safest plan 

 to allow the specimen to soak for two or three days in 

 formaldehyde 2 per cent., and then to change it into 

 formaldehyde 4 per cent. It is a great mistake to be 

 stingy over the formalin ; use it freely, and change 

 the solution at least once, or, if this cannot be done, 

 make up the strength by adding a very small quantity 

 of the strongest formalin. 



There can be no doubt that collectors, as a rule, do 

 not use sufficient formalin, and forget that their speci- 

 mens are very liable to remain untouched for two or 

 three years. Specimens which are worth a place in a 

 permanent collection are worth a little extra trouble 

 and a little extra formalin. 



Concerning the strength of the solutions of formalin 

 for preservation there is a difference of opinion. 

 Some workers use weak and others fairly strong 

 solutions. A good, useful solution for general work 

 is formaldehyde 4 per cent., which is made up thus : 

 Formaldehyde 40 per cent, (or about 40 per cent.), 

 1 part ; water, 9 parts. The bottle may be labelled 

 either " Formalin 10 per cent.," or " Formaldehyde 

 4 per cent." 



If the commercial solution is purchased at 30 per 

 cent, strength, then the following proportions should 



