38 MODERN SCIENCE READER 



cules of hydrogen by nitric peroxide. There are several 

 varieties of pyroxyline which are obtained by using differ- 

 ent mixtures of acid. The highest nitro-cotton product, 

 guneotton, or trinitrocellulose, is useless for the manu- 

 facture of artificial silk, as it is insoluble in a mixture of 

 alcohol and ether. To obtain the pyroxyline or binitrocel- 

 lulose suitable for the production of collodion for our pur- 

 pose, a mixture of 15 volumes of sulphuric (H 2 S0 4 ) and 

 12 volumes of nitric acid (HN0 3 ) is made; two pounds of 

 bleached raw cotton is then taken and put into an earthen- 

 ware jar with about three gallons of mixed acid; this is 

 left standing for four to five hours, when the nitration is 

 complete. The chemical reaction may be expressed by the 

 following formulae : 



C 6 H 10 5 + 2HN0 3 + H 2 S0 4 = 

 C 6 H 8 (N0 3 ) 2 3 + (2H 2 + H 2 SOJ 



The object of the sulphuric acid (H 2 S0 4 ) is to take up 

 hygroscopically the excess of water produced, leaving the 

 nitric acid (HN0 3 ), of which there is always an excess. 

 The only known way of testing the quality of the pyroxy- 

 line is the use of the microscope in conjunction with the 

 polariscope. A small piece of pyroxyline is taken from 

 one of the jars, thoroughly washed in water and dried ; it 

 is then moistened with alcohol, when the colors exhibited 

 should be in exact proportion which practice has proved to 

 give the best results. 



The pyroxyline is now taken out of the pots and sub- 

 jected to pressure to extract all the acid possible. This 

 extracted acid is not wasted, but is renovated with a mix- 

 ture of new acid and used again for more cotton. From 

 the press the pyroxyline is taken to the washing room and 

 at once put into the washing machine, called a hollander, 

 and similar to those used in paper making for washing 

 pulp. 



This washing continues for from 12 to 15 hours until 

 the acid is thoroughly eliminated ; from thence the material 



