214 ULMITK. A COXSTITUBXT OF BLACK SAND.STOXK, 



ami also in strong spirit, giving a solution resembling earamel. The water 

 solution obtained in this way, when treated with barium hydrate or earbonate 

 becomes colourless the substance being carried down along with the 

 barium sulpliate. The dark brown solution obtained by treating a 

 dilute solution of soda or potash with • excess of the substance, is 

 I'eadily preeiintated with alcohol, tlie supernatant liquid having still, however, 

 a fairly dark colour. A solution in potash, on neutralisation with sulphuric 

 acid, avoiding excess, remains clear and is precipitated by addition of alcohol. 

 The precipitate may be thoroughly washed with dilute alcohol (Sp. Gr. O.SO), 

 after which it dissolves readily in water, the solution so formed not being pre- 

 cipitated liy alcohol, Init, if a small amount of potash or soda be added, alcohol 

 produces a copious precipitate, leaving the solution only slightly coloured. The 

 aqueous solution of the alcohol-washed precipitate gives brown precipitates with 

 most metallic salts, precipitation being complete, also with the hydrates and 

 salts of barium, calcium and strontium, with the alums, and with bromine water. 

 Iodine, tannin and starch solutions produce no precipitate. 



Ainong-st the few metallic salts which do not cause a precipitate arc mer- 

 curic chloride and ammoniacal nitrate of silver. The colour is re- 

 moved by shaking with liydrates of iron and alumina and with 

 litliarge, manganese dioxide, animal charcoal and ordinary soil, pi'evious 

 ignition of the soil making no difference. When shaken with 

 sand the solution is decolourised, the colour, however, being absorbed entirely by 

 the fine clayey portion of the sand, the coarser giains being inert. The same 

 applies to treatment with the black sandstone, after ignition, but if sand or 

 soil is boiled with hydrochloric acid and washed so as to remove soluble mineral 

 matters, the residue is quite inert. 



The substance can be salted out of solution with a number of salts, sodimn 

 chloride and sulphate, ammonium sulphate, nitrate and chloride and others, 

 leaving tlie solution but faintly coloured. From concentrated solution?, acetic 

 aci<l causes practically corajdete precipitation in a well curdled form, but from 

 dilute solutions the precipitate is slimy but equally complete. 



The barium compound prepared by precipitating the water soluble prepara- 

 tion with baryta water, washing with alcohol, and drying, corrected for asso- 

 ciated mineral matter, contains 41.3 per cent, barium oxide. 



The imlverised air-dry rock yielded the following figures to jiroximate 

 analysis : — 



Water I.(i3 



Loss on ignition 8.1!) 



Sand 89.50 



Soluble in liydrochloric acid -RS 



100.00 

 When the coating from the bl.ack sandstone is lixiviated until (luite free 

 from sand and air-dried, it has the Inllowing proximate com))osition : — 



Water at 150° C IT.3 



Loss on ignition ''^-(^ 



Mineral l''"'-! 



100.0 

 On boiling 0.5 gram with .50 c.c. N/IO caustic soda and titrating back 

 with corresponding sulphuric acid, 24.7 c.c. of neutralisation was obtained. 



