MANUFACTURE OF OXALIC ACID 171 



of artificial sili<. Silk is a peculiar variety of cellulose; all plant matter containing cellulose, and notably 

 all wood fiber may be used for the manufacture of artificial silk. 



The adaptability of the various American forest trees to the production of artificial silk remains to be studied. 



The price of artificial silk approximates ^I'SSperlb.; whilst the price of natural silk varies between 

 ^4-00 and -ve-OO per lb. 



Artificial silk is used on a daily increasing scale in silk weavings. New methods and modifications 

 of manufacture continuously increase its chances to become a substitute for natural silk. 



(C) PROCESSES OF MANUFACTURE. There are three main processes in use, namely: - 



I. A solution of nitro-cellulose, a compound of nitric acid and cellulose in ether or alcohol, is pressed 

 through minute capillary pipes, appearing in long, silky threads. The methods of Vivier and Lehner reduce 

 or entirely destroy the inflammability of the product. 



II. Cellulose is dissolved in a mixture of copper oxide and ammonia. This solution forms a waxy 

 mass which is pressed through minute capillary openings and appears in the form of supple, long, silky 

 threads, immediately entering a bath of sulphuric acid. Here cellulose is set free, now a solid thread, 

 while blue vitriol and sulphate of ammonia result at the same time. The threads are spun exactly like 

 threads of natural silk. 



III. Viscose process. A combination of cellulose and sodium, treated with carbon-bysulphide, yields 

 a glutinous, cartilaginous substance of great pliability, first produced in 1892 and named "viscose." 



Exposed to the influence of the atmosphere, carbon-bysulphide is set free, gradually, through 

 evaporation. 



From the substance remaining, from which the sodium is removed by washing, a peculiar variety of 

 cellulose is obtained, technically known as "viscoid." 



Viscose can be treated to coloring matter, and the viscoid retains the color thus imparted. 



When a solution of viscose is forced through minute, capillary pipes, finer threads may be obtained 

 than those produced by the silkworm. These threads, deprived by rapid evaporation of the carbon- 

 bysulphide adhering to them, or else passed to the same effect through a solution of chloride of ammonia, 

 are so fine that they cannot be used individually, and that strands of them must be used for spinning 

 and weaving. 



Viscose silk is no more inflammable than is cotton. 



PARAGRAPH XXXVlll. 

 MANUFACTURE OF OXALIC ACID. 



(A) PRINCIPLE. Any wood heated to about 400 degrees F. in the presence of caustic substances 

 yields, among many other products of disintegration, a large percentage of oxalic acid. 



(B) RAW MATERIAL. Any wood finely ground or pulverized, and especially sawdust and mill refuse, 

 is well adapted to the process, -oak as well as beech, pine, chestnut, &c. Cottonwood is said to form 

 a poor raw material. 



(C) PROCESS. A mixture of caustic soda, caustic potash, and sawdust is heated, under continuous 

 stirring, in open pans ('/, foot deep and 6 feet square). The temperature is gradually raised to 480 degrees (not 

 over)F., remaining at that figure for about I'/s hours. The melted mass, consisting of oxalate of sodium 

 and of carbonate of potassium, is thrown into water and allowed to cool, when the oxalate forms a dough 

 of minute crystals. This dough is freed from water by centrifugal power, then treated with lime and thereafter 

 with sulphuric acid, with the result that gypsum is precipitated from a solution of oxalic acid. 



(D) OUTPUT. One hundred parts of wood yield up to 80 parts of oxalic acid. The quantity of the output 

 depends on the proper mixture of caustic soda and potash, and on the proper regulation of the temperature. 



(E) USE. Oxalic acid is used in calico printing, in bleaching, and in polishing metals. Some of its 

 salts are used in photographic developing. 



