32 Dehydration (chap. 2) 



manner: if a 70% solution is required, measure 70 parts of 95% alco- 

 hol and add 25 parts of distilled water to make 95 parts of 70% dilution. 

 In other words, into a 100 ml. graduated cylinder pour 95% alcohol to 

 the 70 ml. mark, and then add distilled water up to the 95 ml. mark. 



Absolute alcohol is not accurately 100%, but may contain as much 

 as 1 or 2% water. If the water content is no higher than this, the abso- 

 lute alcohol is considered 100% for practical purposes in microtech- 

 nic. If it is necessary to make certain that the water content is no 

 more than 2%, add a few ml. of the alcohol to a few ml. of toluene or 

 xylene. If a turbidity persists, there is more than 2% water present. But 

 if a clear mixture remains, the alcohol is satisfactory as an absolute 

 grade. 



Dilutions of isopropyl alcohol (99%) can be handled as a 100% solu- 

 tion; that is, for 70% use 30 ml. water to 70 ml. of alcohol, etc. 



If distilled water is not provided in the laboratory building, a Barn- 

 stead Still ^ can provide a sufficient amount of water for an average 

 microtechnic laboratory. The stills are available in sizes of i^ up to 

 10 gallons of water produced per hour. A special model will produce 

 30 gallons per hour. 



Special Treatment for Small, Colorless Tissues 



Often a tissue is small and lacking in color, and seems to disappear 

 into the opaqueness of the paraffin. An easy answer to this problem is to 

 add some eosin to the last change of 95% alcohol; the tissue can then be 

 seen more readily and oriented with greater facility. This, however, 

 cannot be done if isopropyl alcohol is being used, since stains are not 

 soluble in it. The eosin will not interfere with future staining; it is lost 

 in the hydration series following deparaffinization. 



^ Barnstead Still and Sterlizer Company, 49 Lanesville Terrace, Boston 13, Massachusetts. 



