THE INDIA RUBBER WORLD 



[August 1, 1916. 



d. its 

 This 



SELECT METHODS OF ANALYSIS OF GOLDEN SUL- 

 PHIDE OF ANTIMONY. 



GOLDEN sulphide of antimony, or antimony pentasulphide, 

 is a product of prime importance for the vulcanization of 

 many rubber articles, notably for automobile inner tubes and 

 surgical sundries. 



The preparation of antimony penta.sulphi<lc is very delicate 

 and if the different phases are not conducted witli every re- 

 quired precaution, there is risk that a product will be obtained 

 which w'M possess none of the qualities required in rubber 

 manufacture. Pure pentasulpliide of antimony is both an 

 orange red pigment and a vulcanizing agent. It is capable, at 

 the ordinary temperatures of vulcanization, nf partially de- 

 composing, with the lilieraticn of 2 molecules of .sulphur, liccnm- 

 ing reduced to the red or trisulpliide of antimony. 



According- to the method of its preparation, it is capable of 

 carrying more or less free sulphur, besides antimonious acid, 

 antimoniates, red trisulphide. oxysulphides of antimony and of 

 sulphate of lime. 



Besides these substances, which are legitimate impurities of 

 manufacture, there may be found flowers of sulphur, added 

 mechanically, vermilion or red sulphide of mercury and oxide of 

 iron added to produce a to!\e 



Before using it one should sulmiit it to a thorough analysis 

 to determine its exact contents of free sulphur and actual 

 lientasulphide. 



True golden sulphide should contain only antimony and sul- 

 phur. It should be neutral or slightly alkaline. Il 

 color deepens, loses its clearness and becomes 

 defect of acidity is one by which one is able to detect hurried 

 manufacture and insufficient or hasty washing. 



It should be very nearly impalpable and perfectly dry, a con- 

 dition difficult to attain, except liy vacuum drying process, be- 

 cause the drying temperature must not exceed 70 degrees C. 



\arious methods have been iiroposed for the analysis of golden 

 sulphide, and some of them readily furnish knowledge of the 

 commercial products on the market. 



They are summarized below : 



KKEK SI l.l'iHK 



To use intelligently a .golden sul|iliide, it is always necessar\- 

 to know its free sulphur. 



llerbst's Method.— .\ known weight of pentasul|)hide is ex- 

 tracted in a Soxhlet by freshly distilled sulphide of carbon for 

 S or 10 hours. The sulphur solution is transferred to a tared 

 beaker, evaporated on a water-bath and sulpluir weiglied after 

 drying in an oven at I0() degrees C. 



Weber's Method.— .^mmonia dissolves the pentasulphide of 

 antimony at a moderate temperature. .\ntimony oxide and 

 free sulphur are insoluble. 



.\ quantity of golden sulphide is dissolved in concentrated 

 ammonia, gently heated on a water-bath, thrown on a tared fdter 

 and the residue washed with ammonia until the liltrate will 

 no longer precipitate pentasulphide by acidifying. 



Tlie insoluble residue is dried at 60 degrees C, and extracted 

 for 6 hours with freshly distilled sulphide of carbon. 



The residue on the lilter is practically antimonious acid which 

 can be dried and weighed. 



The bisulphide of carbon ns.-.l for the extraction is evaporated 

 on a water-bath, the residue is dried at 60 degrees C and the 

 sul[ihur weighed. 



This method is long, but if the pentasidphide dissolved in 

 annnonia is reprecipitated by acid, filtered and dried, one is able 

 to determine by the same analysis the free sulphur, pentasulphide 

 and antiiTionious acid. 



(■(i.vinixi'.i) .stT-PiiUK, 



Caspari's Method. — The analysis is made on a lialf gram 

 sample from which the free sulphur has been removed by carbon 



bisulphide. The extracted antimony sulphide is added gradually 

 into 5 ce. pure nitric acid in an Erienmeyer flask and the mix- 

 ture cooled by immersion in water. The antimony is thus com- 

 pletely oxidized, but a certain quantity of the sulphur remains 

 in the form of yellow masses. The flask is then slowly heated 

 by immersion in boiling water, care being taken to guard against 

 the fusion of sulphur. From time to time a pinch of potassium 

 chlorate is added, until all the sulphur has disajjpearcd. 



Tlie tTiixture is then transferred to a dish and evaporated to 

 dryness. 



The residue is taken u\< in -100 ce. of boiling water, with ad- 

 dition of a little tartaric acid, to keep the antimony in solution. 

 The sulphuric acid formed is determined, in the usual way, as 

 barium sulphate. 



.\,\|].MI).\V. 



Caspari's Method. — The determination of antimony should be 

 conducted on a sample from which the free sulphur has been 

 extracted, because it otherwise prevents the solution of the anti- 

 mony sulphide in the acids. One-half gram of sulphur-free 

 pentasulphide is dissolved in 10 cc. of hydrochloric acid and the 

 sulphureted hydrogen expelled by boiling ; 2.2S grams of tar- 

 taric acid and 200 cc. of water are added and the whole boiled. 

 .\ny residue of silica should be Idtered from the solution on -a 

 tared lilter, dried and weighed. The antimony tartrate in the 

 fdtrate is precipitated as antimony sulphide by a current of 

 hydrogen sulphide. The antiinony sulphide is transferred to a 

 large porcelain crucible and 3 cc. nitric acid is added to it. The 

 crucible must be covered to prevent loss. 



When the action is over, the mass is evaporated until dry, 

 by immersion of the crucible in boiling water; then a few drops 

 of nitric acid are added tn the residue and the crucible is heated, 

 first, slowly, over a small Hame, then more powerfully, to expel 

 the sulphur and the acid, and, lastly, calcination is effected. The 

 antimony present is weighed as SbO, and calculated as penta- 

 sulphide. 



WATER. 



Aloistiire is determined by drying 10 grams of pentasulphide 

 either in a vacuum oven or in an ordinary oven in a current of 

 nitrogen at a temperature not exceeding 60 degrees C. Tlie 

 percentage of moisture present should not exceed one per cent. 



VERMILION. 



The pentasulphide is totally soluble in ammoniutn sulphide 

 without the application of heat, while vermilion is not soluble. 

 In this manner these two substances can be separated. 



After washing, the vermilion precipitate is dried and weighed. 



If a commercial golden sulphuret contains pentasulphide, red 

 trisulphide and vermilion, an aliquot part is first treated by cold 

 ammonium carbonate which dissolves the trisulphide and leaves 

 the pentasulphide and the vermilion. Then the residue is treated 

 with cold ammonium sulphide which dissolves the pentasulphide 

 and leaves the vermilion. 



RUBBEK COMPOUND TO REPLACE SEALING WAX. 



.\ patent has been recently granted for a material that is flex- 

 ible, adhesive and an excellent substitute for common sealing 

 wax. It is composed of the following ingredients: 

 Grains. 

 K>sin (c 



uliber 



For coloring, 40 grams of vermilion are added. The resin is 

 first dissolved in a copper vessel and the other ingredients then 

 added and the whole well stirred over a hot fire. The melted 

 mixture is then poured into molds and when cool, the cakes are 

 removed and allowed to cool for 24 hours on a marble slab. 

 [Ramon Castello, Provenza 240. Barcelona, Spain. British Pat- 

 ent No. 7,703 (1915).] 



