CHEMICAL INVESTIGATION. 



21 



increase in weight. An external characteristic which should also be 

 noted is color. A great deal of information regarding the constitution 

 of a liber is ascertained by this process. 



Carbon percentages from combustion. — This process consists in burn- 

 ing the substance with chromic anhydride in presence of sulphuric 

 acid and leading over the gaseous products (CO and C0 2 ) into an appa- 

 ratus in which their volume can be exactly measured. The two oxides 

 of carbon having the same volume, the quantity of carbon in unit 

 volume is independent of the composition of the gas, which therefore 

 only requires to be measured. The carbon in the typical (cotton) cellu- 

 lose is 44.4 per cent; the compound celluloses, on the other hand, range 

 themselves for the most part into two groups — (1) of lower carbon per- 

 centage (40-43), (2) of higher (45-50), in the former the pecto-celluloses 

 are included, the ligno-celluloses in the latter. This is considered a 

 prominent chemical constant of the fiber substance. 



Acid purification. — The object of this treatment is to clean the fiber 

 and remove accidental impurities, while occasioning the minimum loss 

 of weight and therefore alteration in composition. For this purpose 

 acetic acid (20 per cent) is chosen, the fiber being heated with the acid 

 to the boiling point, then removed and washed first with alcohol and 

 lastly with water, dried, and weighed. The loss in weight sustained is 

 thus determined. It is in the fiber thus purified that the carbon per- 

 centages are determined. 



In a report on the miscellaneous fibers in the Colonial and London 

 Exhibition of 1886, by C. ¥. Cross, the scheme of analysis is thus 

 briefly stated in tabular form : 



r Moisture Hygroscopic water, or water of condition. 



Ash Total residue left on ignition. 



Hydrolysis (a) Loss of weight on boiling raw fiber five 



minutes in 1 per cent solution of caustic 

 soda. 



Hydrolysis (&) Loss of weight on continuing to boil one 



hour. 



Cellulose White or bleached residue from following 



treatment: (1) Boil in 1 per cent NaOH 

 five minutes ; (2) exposure to chlorine gas 

 one hour; (3) boil in basic sodium sul- 

 phite. 



Mercerizing Loss on treating one hour with 33 per cent 



solution caustic potash, cold. 



Nitration Weight of nitrated product obtained by 



treatment with mixture equal volumes 

 of nitric and sulphuric acids one hour, in 

 the cold. 



Acid purification .. .Raw fiber boiled one minute with acetic 

 acid (20 per cent), washed with water and 

 alcohol, and dried. 



Carbon percentage.. The carbon in the fiber from above, deter- 

 mined bv combustion. 



Separate portion 

 taken for each 

 determimation. 

 Results calcu- 

 lated in percent- 

 age of dry sub- 

 stance. 



