APPENDIX 221 



The difficulties in the way of using these tables, which 

 may at first seem great, will be easily overcome by tracing 

 three or four specimens through to their proper families. 



III. REAGENTS IN COMMON USE. 



Only the most common reagents are given, as it is sup- 

 posed that the teacher will have access to technical books 

 for all delicate experiments and tests. 



Alcohol. — As commonly obtained for laboratory pur- 

 poses, alcohol is ninety-five per cent. pure. This may be 

 diluted to the required strength by calculating the amount 

 of water to be mixed with ninety-five per cent, alcohol to 

 produce the amount of liquid required. It may be obtained 

 for school purposes free of internal revenue by complying 

 with certain formalities required by law. Such alcohol 

 is of the best quality — ninety-five per cent, generally — 

 and can be obtained at a great reduction from the regular 

 retail price. For information address Secretary of the 

 Treasury, Washington, D. C. 



Formalin. — This is a hardening agent, which has much 

 the same effect on hardening tissue that alcohol does, ex- 

 cept that it expands the tissue slightly. For all general 

 purposes it is equal to alcohol and has the adidtional ad- 

 vantage of being much cheaper. It is used in strength 

 from one to two per cent solution in water. 



OsMic Acid. — One and one-half to two and one-half per 

 cent, solution used for killing microscopic animals. It 

 should be kept in the dark and should be diluted with water 

 when used. 



