TBANSACTIONS OF SECTION B. 515 



ing power or " body " is not comparable with the latter. Next, an ingenious white 

 or stone-coloured paint was economically produced from oxide of antimony by 

 Dr. Stenhouse, which appeared to answer very well in certain circumstances. I 

 myself have made a great number of experiments with the view of utilising some 

 of the artificial silicates, such as those of lime, magnesia, and zinc, &c, which 

 possess a very brilliant white colour, by submitting them to a great variety of 

 treatments ; but I have been unsuccessful in imparting to them anything like the 

 " body " of white lead ; they all become more or less translucid when mixed with 

 oil, like pure silicic acid itself, whatever mechanical treatment they may have pre- 

 viously undergone. 



"Whilst occupied with these researches I learned accidentally that Mr. Thomas 

 Griffiths, of Liverpool, had obtained a new pigment, the basis of which was the 

 white sulphide of zinc, and on submitting this new product to examination I 

 found, with considerable astonishment, that it surpassed the ordinary white lead 

 in every respect, in colour, in resistance to the weather and gaseous emanations, 

 and in durability ; moreover, that it was not destructive to the health of the work- 

 men who manufacture or who use it. Mr. Griffiths has been experimenting, I 

 understand, for about ten years upon the best means of producing this new mineral 

 white upon a large scale, and has, apparently, now brought its preparation to a 

 state of perfection which has gone beyond the most sanguine expectations. 



A salt of zinc, which may be the sulphate or the chloride, is precipitated 

 by a soluble sulphide ; the latter being either sodium, calcium, or barium sulphide, 

 or a mixture of them ; precautions are taken to avoid the precipitation of any 

 black sulphide of iron, if perchance the zinc solutions contain a little of that metal ; 

 the bulky product is collected, dried, and transferred to a furnace, where it is 

 calcined for some time at a cherry red heat. During the calcination it is carefully 

 stirred to bring each portion successively in contact with the air ; it is then raked 

 out whilst quite hot into vats of cold water, where it is levigated, and afterwards 

 collected and dried. 



The result is a white pigment of exquisite beauty. Its covering power, when 

 mixed with oil, is greater than that of any substance hitherto discovered, being 

 about 25 per cent, higher than that of the same weight of pure carbonate of 

 lead. 



According to my analysis, this new product is really an oxy-sulphide of zinc, 

 the composition of which varies somewhat according to the length of the cal- 

 cination and the heat attained. Hence it is a difficult matter to get it exactly of 

 the same composition at each successive operation. Nevertheless, this is attained 

 quite closely enough for practical purposes. The best product appears to correspond 

 in composition as nearly as possible to the formula, 5ZnS + ZnO. But occa- 

 sionally a larger quantity of oxide is produced and the product by means im- 

 proved thereby. 



In some experiments which I made for the purpose of testing the capabilities 

 of this new white pigment, as compared with the old zinc white (oxide of zinc), 

 and white lead (pure carbonate of lead), I was perfectly surprised at the results, 

 my own experiments made with the view of discovering a substitute for the latter 

 having proved such utter failures, and I look upon this new oxy-sulphide of zinc 

 pigment as one of the most interesting products hitherto derived from mineral 

 chemistry. As it possesses much more covering power than the old zinc white, or 

 oxide of zinc, it is considerably more economical than the latter. As to white 

 lead, it has only one recommendation as a colour, namely, its great " body " or 

 covering power ; but it is liable after a time to saponify the oil, producing a soap 

 which is more or less translucid ; moreover, it is darkened by gaseous emanations 

 and it is detrimental to health. The new product possesses none of these draw- 

 backs. It has all the covering power of white lead, combined with permanency 

 in colour, and resistance to the saponifying influence of the oil, and is a much finer 

 white. Nothing more is requisite but to ensure for it a constant composition, and 

 I have little doubt that this difficulty will be overcome in the course of a short 

 time. 



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