HEAT OF VAPORIZATION 89 



not unite with the alcohol. The alcohol is then dis- 

 tilled again and is 95 to 98 per cent pure, and this is 

 called absolute alcohol. 



Wood alcohol is made by the dry distillation of wood. 

 The wood is placed in an air-tight retort and heated. 

 Wood alcohol is extremely poisonous, and when it is 

 burned formaldehyde is produced, which is very hard on 

 the eyes; CHgOH (Methyl Alcohol) + O (Oxygen) = 

 HCOH (Formaldehyde) + H 2 O (Water). Some labora- 

 tory men have become blind by continuous use of wood 

 alcohol as a heat producer. 



The alcohols which are made by the yeast plant from 

 grain or fruit juice and purified by distillation are also 

 poisonous, but not so much so as wood alcohol. As 

 beverages, alcoholic liquids are recognized as neither neces- 

 sary nor desirable for the best of health. Many well-known 

 physicians do not prescribe them for medicines. 



Denatured Alcohol is grain alcohol made more poison- 

 ous by adding about 10 per cent of wood alcohol or other 

 poisonous liquid, so that it cannot be used for beverage 

 purposes. 



63. Fractional Distillation is a process by means of 

 which mixed substances, each having a different boiling 

 point, are separated from one another. This is done by 

 heating the mixture to the boiling point of each substance 

 in succession and catching the condensed vapor in sepa- 

 rate vessels. The many products of petroleum are 

 obtained in this way. Rhigolene, which boils at a tem- 

 perature of between 20 and 25 C., is the first to vaporize 

 and pass off. This is followed by petroleum ether, boil- 

 ing at between 50 and 60 C. Then conies gasoline, 

 which boils at 70 to 90 C.; then naphtha, boiling at 

 between 90 and 120 C.; followed by benzine, boiling at 



