I06 PHILOSOPHICAL TRANSACTIONS. [aNN0 1771. 



Xf^. Experiments to shoio the Nature of Aurum Mosaicum. By Mr. Peter 



TVoulfe, F.R.S. p. 1 14. 



After describing various processes (with observations thereon) for making 

 aurum mosaicum (sulphuretted oxyd of tin) which in the present improved state 

 of chemical knowledge it would be useless to retain in these Abridgments, Mr. 

 W. subjoins the following account of an apparatus for making aurum mosaicum 

 in the cheapest manner. 



A glass vessel cannot be used for this operation more than once, because it is 

 necessary to break it to get out the aurum mosaicum. The following utensil 

 may be employed a great number of times, and save the expence of glass. Take 

 a black lead crucible, N° 60; bore a round hole in its bottom about 3 inches dia- 

 meter; and saw off an inch of its upper edge ; if it has a lip, get a round piece of 

 burntclay, of an inch thick or rather more, to fit exactly into this edge; the com- 

 position, which is used for making paving-tiles, answers very well for this purpose. 

 In order to make use of this apparatus, fit the round piece of burnt clay to the 

 inner edge of the crucible, by means of some loam softened with glue, and dry 

 it slowly ; then turn it upside down, and lay it in a proper furnace on 2 iron bars. 

 The mixture* for the aurum mosaicum is to be put in through the round hole at 

 top, and then covered with an aludel and luted; this serves to collect the flowers 

 and the sublimate which rises. The fire is to be made under and all round the 

 crucible. 1 1 lb. Troy of aurum mosaicum may be made here at a time ; and 

 when the operation is over, the bottom or round piece of burnt clay will easily 

 come out with the aurum mosaicum. A large crucible may be made use of, if a 

 larger quantity be required to be made at once. The operation cannot fail of 

 success, provided the fire be made of a sufficient strength, and of an equal de- 

 gree from the bottom to the top of the crucible, which is easily done in a good 

 furnace. The operation is finished in 8 hours, unless the volatile liver is wanted. 



White arsenic, digested with a solution of tin in the acid of salt, becomes 

 soon black ; it hereby regains its phlogiston, and is reduced to the taste of regu- 

 lus of arsenic, and will by this means readily combine with copper, and other 

 metallic substances ; which it would not do without the help of phlogistic sub- 

 stances. This is the most easy and ready way of reducing arsenic to its metallic 

 form : the arsenic may be deprived of the solution of tin, which adheres to it, by 



• The mixtnre recommended for the preparation of aurum mosaicum by Mr, W. is as follows : 

 tin, 12 oz.j sulphur" oz. ; sal ammoniac, 3 oz.; mercury, 3 oz. From this mixture (varied from 

 the formula in the Lond. Pharmacopofiia of that day) he obtained 17s oz. of aurum mosaicum ; but 

 Mr. W. showed by other experiments, that mosaic gold could be prepared without employing either 

 mercury or sal ammoniac. The celebrated French chemist, Mons. Pelletier, has since shown that 

 aurum mosaicum may be obtained by a very short and simple process j viz. by subjecting to a proper 

 degree of heat equal parts of oxyd of tin and sulphur; thus demonstrating its composition, viz. tha' 

 it is a sulphuretted oxyd of tin. 



