THE INDIA RUBBER WORLD 



lAi'Rii. 1. 1919. 







1® 



Fig. 7 — Typical Layout Making-Up Room. 

 :100-Watt Mazda C Lamp ix RLM Standard Domh 



cult njieratKiii can be performed willi ca.sc. Skiving is no doubt 

 the step of manufacture which falls under this classification and 

 with a scheme such as outlined, it can be readily accomplished. 

 VARNISHING AND VULCANIZING. 

 Here again the work is more or less handled in bulk although 

 it is practically a finished product. There are no demands for 

 close vision and a low intensity of general illumination will 

 suffice. This can be supplied with 20O-watt lamps on 20-foot 

 centers if the ceiling is high, or 100-watt lamps on 14-foot cen- 

 ters or 75-watt lamps on 11-foot centers in the case of a low 

 ceiling. 



INSPECTING AND PACKING. 



To prevent defective material getting in tlie hands of the 

 customer, it is well to have this room brightly lighted so that 

 all imperfectations are clearly discernible. The high intensity 

 of general illumination from 100-watt lamps on approximately 

 10-foot centers is essential. Where piles of material extend 

 close to the ceiling, outlets should be located with reference to 

 these so that bad shadows are eliminated. 



Analysis of Antimony Pentasulphide. 



By D. Repony. 



AFTER having tried to analyze antimony pentasulphide, fol- 

 lowing the known methods, in no case could perfect results 

 be obtained. Either the method required too much work 

 or was not in accordance with the need of the rubber manufac- 

 turer. By most methods the main object is to determine the to- 

 tal antimony content. It is, however, altogether wrong to value 

 the antimony pentasulphide by high content of antimony, the 

 essential thing being that the product should show a high per- 

 centage of antimony pentasulphide. 



Commercial antimony pentasulphide is produced by treating 

 the mineral stibnite with sulphur and lime, obtaining calcium 

 thioantimonate, which is decomposed by sulphuric acid into 

 antimony pentasulphide and calcium sulphate. After the anti- 

 mony compound is washed with water to remove the free acid 

 and some of the water-soluble calcium sulphate, a large quan- 

 tity of calcium sulphate still remains with the product. 

 When, however, caustic soda is used in the reaction instead 

 of lime, the antimony obtained is free from calcium sulphate, 

 providing the product has been thoroughly washed. Thus the 

 presence of calcium sulphate must not be considered as an adul- 

 terant but as a by-product of the reaction. The writer has found, 

 also, all kinds of adulterants admixed with the antimony. The 

 adulterants are mostly red oxide of iron and iron silicates, such 

 as red clay, whiting and barytes. Therefore, to analyze for 

 adulterants is considered very essential. 



Before any attempt is made to analyze antimony submitted 

 for rubber compounding it should be tried practically in some 

 of the most important rubber compounds, replacing the same 

 quantity of satisfactory lots previously used, and the rubber 

 compound be subjected to a series of different heats of vul- 

 canization. Should the rubber compound not change color dur- 

 ing the vulcanization at 310 degrees F., it is probable that the 

 antimony will show satisfactorily on aging. Should the color 

 change on vulcanization at the above temperature and also at 

 lower heat, further consideration will depend very much upon 

 the price quoted and the quality of the rubber goods in which 

 it is to be used. In cheap compounds generally the same shade 

 of red which is obtainable by poor antimony can be readily 

 duplicated with red oxide of iron. Should the antimony show 

 satisfactorily in rubber compound under the heat of vulcaniza- 

 tion, the next thing is to prove that it contains some adulterant. 

 TEST FOR ADULTERANTS. 



Take about five grams of the sample in 100 cc. of ten per cent 

 hot caustic soda solution, and stir with a glass rod on a steam 



antimony tetraoxide, whitmg. 



for the analysis of antimony 

 results from the point of view 



bath till no red particles can be observed; this usually requires 

 ten minutes. Pure antimony should dissolve completely. Any red 

 powdery residue indicates an adulterant, such as red oxide of 

 iron or iron silicates. A white residue indicates, in most cases, 

 calcium sulphate, which can be readily confirmed. If the residue 

 is not soluble in cold water it i 

 barytes. silica, etc. 



The method described below 

 pentasulphide yields satisfactory 



of the rubber manufacturer, and affords the analyst partial 

 formation with the least work, or, where time and facilities are 

 available, the complete analysis may be effected. 



METHOD FOR COMPLETE ANALYSIS OF ANTIMONY 

 PENTASULPHIDE. 



The antimony should be neutral and about 420 specitic gravity. 

 The crimson antimonies are mostly of slightly acid reaction. 

 However, the acid content must be in any case not higher than 

 1/100 of one per cent. The acidity is determined qualtitatively 

 by wetting a little of the sample with water and testing it with 

 litmus paper. The quantitative amount of the acid contained 

 in the sample should be determined in the following manner: 

 Take two grams of the sample, place it in filter, and wash it 

 with water till the washing water is neutral ; then titrate the ob- 

 tained solution with 1/10 normal caustic soda, using phenol- 

 phthalein as indicator. Antimony containing more than 1/100 of 

 one per cent of free acid should be rejected, as this is apt to 

 cause blisters during vulcanization, especially in such rubber 

 compounds as contain carbonates. Crimson antimony very sel- 

 dom contains free sulphur. The amount of free sulphur in 

 orange antimony ranges from none up to 30 per cent, the usual 

 amount being between 15 and 20 per cent. 



To determine free sulphur place five grams of the sample in 

 a thimble of filter paper in such manner that the solvent 

 during extraction cannot splash out any of the antimony. Fresh 

 redistilled carbon disulphide must be used as solvent, and the 

 extraction be continued for ten hours ; this should be done over 

 night. 



The following precautions should be noted. Carbon disul- 

 phide when not freshly distilled usually contains much free 

 sulphur, and if used in extracting will lead to false results in 

 the analysis. Also carbon disulphide readily decomposes under 

 the influence of light, especially during boiling. The writer has 

 observed that this result during day-time extraction is variable. 



