476 Progress of Invention. 



removed, and is well stirred in. A plate of zinc is then introduced 

 into the mixture, and is made to come into contact with the copper 

 vessel, at as many points as possible — the surface of the zinc being 

 about equal to half that of the copper. The current of electricity 

 thus produced causes a foaming, which is great in proportion to the 

 amount of impurity ; and the gelatinous constituents are dissipated 

 in the form of gas, or are retained in the water, and removed when 

 the action ceases. After the fat has been drawn off, it is allowed to 

 settle ; and, having been separated from the matters which subside, 

 it is filtered, after which it is quite pure, and ready for sale or use. 



ISTew Mode of Whitening Wool. — The beautiful white wool 

 produced in this country has long been the envy of continental 

 manufacturers, and many attempts have been made to rival it, not 

 altogether without success. A process recently invented in 

 Germany seems to have left nothing further to be desired on the 

 subject. The wool to be bleached is steeped in a strong neutral 

 solution, containing sulphate of magnesia, amounting to the one- 

 twentieth of the weight of the wool ; and this solution is decom- 

 posed by the addition of bicarbonate of soda, equal to seven-tenths 

 of the weight of the sulphate of magnesia — the mixture being then 

 gently heated to about 90° Cent. Basic carbonate of magnesia 

 precipitates, and the larger portion of it attaches itself to the fibres 

 of the wool, rendering them extremely white, without impairing 

 their softness ; carbonic acid is evolved. 



Novel Application op Capillary Attraction. — Capillary 

 attraction has been applied by M. Duclos to the reproduction of 

 drawings, etc., by means of processes which are founded on the 

 fact that, if a silvered plate of copper is written on with an unctuous 

 or resinous substance, and afterwards subjected to the action of 

 mercury, that fluid will adhere to the uncoated portions and form 

 projections rising considerably above them ; so that, even when 

 the excess of mercury is carefully removed, it will still remain in 

 relief, and a copy of the plate in this condition can be taken, from, 

 which maybe obtained an electrotype that, if printed from, will 

 afford a fac-simile of the drawing. M. Duclos, in practice, replaces 

 the mercury by a compound consisting of fusible metal and mercury. 

 When this is melted and poured over the silvered plate on which 

 the drawing has been made, it comports itself exactly like the 

 mercury ; but, being harder, when cold, an electrotype may be ob- 

 tained from it directly. When, however, this compound is used, 

 great care must be taken to prevent oxidation, which would be, at 

 a subsequent period, highly inconvenient ; hence the plate is im- 

 mersed in sufficiently heated oil, when the fused metal is being poured 

 upon it. An amalgam of copper, applied to the silvered plate by 

 means of a roller of silvered copper, is also used instead of the 

 mercury ; and when it sets, an electrotype may be had from it. 

 Various modifications are employed when plates for surface printing, 

 etc., are required. 



Photographic Engraving. — Photography has been applied in a 

 novel way to the production of engravings. A photograph is first 

 obtained. For this purpose some good fabric of silk is immersed 



