36 



METHODS IN PLANT HISTOLOGY 



Be very sure that bottles or Stenders for absolute alcohol are perfect- 

 ly dry; also, keep the bottles well corked and keep the lids on the 

 Stenders. The importance of excluding moisture cannot be exagger- 

 ated. Tightly fitting corks and closely fitting covers are better than 

 absorbents; prevention is better than cure. 



The lower grades are made up from 95 per cent alcohol. 



Formulas for alcohols — The following formulas will enable anyone 

 to make the other grades of alcohol from 95 per cent alcohol and water. 



95 95 95 95 95 95 95 95 95 

 10 15 20 30 40 50 60 70 85 



85 



80 



75 



65 



55 45 35 25 



10 



The foregoing are the formulas for various alcohols from 10 to 85 per 

 cent. The fh'st column shows the formula for making 10 per cent al- 

 cohol. The percentage of alcohol secured in each case is indicated by 

 the middle number in each column. In the first formula, subtract 10 

 from 95; the result, 85, is the number of cubic centimeters of water 

 which must be added to 10 c.c. of 95 per cent alcohol in order to obtain 

 10 per cent alcohol. The mixture contains 95 c.c. of 10 per cent alco- 

 hol. If more or less than 95 c.c. of the mixture is needed, take propor- 

 tional parts of 10 and 85. This simple method is a time-saver, but if 

 the bottles or Stender dishes are to be filled frequently, 

 it will be a still further saving of time to use a long label 

 (Fig. 15) and, after pouring in the 95 per cent alcohol, 

 draw a line showing how high it reaches; and then, after 

 pouring in the water, draw another line. The next time it 

 is necessary to fill the bottles merely pour in 95 per cent 

 alcohol until it reaches the first line, and then pour in 

 water until it reaches the second line. It is not necessary 

 to use distilled water if pure drinking-water is available. 

 Synthol is used like alcohol, and many believe it to be 

 a good substitute. 



Acetone has also been used with more or less success 

 for all grades except absolute alcohol. 



Some investigators use more or less complicated dif- 

 fusion apparatus and make the dehydration process ex- 

 tremely gradual. Judging from the finished preparation, we find no ad- 

 vantage in the method. In the diffusion process, the solution is con- 

 stantly changing. This may not be an advantage. 



Fig. 15.— 

 Label for stain- 

 ing-dish. 



