METALS. 



485 



the quantities obtained. " I do not think I exagger- 

 ate," he remarks, " in saying that in my first obser- 

 vation I possessed at the most TSS of a milligramme 

 of the new substance dissolved in a very small drop 

 of liquid. The spectral analysis of so small a quan- 

 tity of matter would have been impracticable before 

 the considerable reduction I made in the dimen- 

 sions of the apparatus for obtaining electric spectra, 

 and without using very small sparks. If, as I sup- 

 pose, there is no error as to the nature or my alum 

 of Ga, the existence of this salt fixes the atomicity 

 of the new element, and attributes to its oxide the 

 same chemical function as that of alumina. The 

 oxide of gallium, then, will be written Ga 2 3 ." 



Separation and Purification of Metals. The 

 principle of Pattinson's process for the separa- 

 tion of alloyed silver and lead depends upon 

 the fact that the one body crystallizes before 

 the other, at the moment of partial solidifica- 

 tion at a low temperature. The same principle 

 has been found applicable to the separation of 

 other metals whose degree of fusibility may be 

 different. It may be taken as generally true 

 that foreign metals will be held suspended in a 

 crystalline condition in the liquid mass of any 

 metal which may have a lower point of fusion 

 than themselves, provided that the tempera- 

 ture of the liquid bath at the time be lower 

 than the melting point of the foreign metals. 

 The foreign crystallized metals may be then 

 separated mechanically from the liquid bath by 

 filtering. A foreign engineer, M. Curter, has 

 sought to apply this principle to the purifica- 

 tion of Bohemian tin, to enable it to compete 

 successfully with the English or Australian 

 qualities. He sought also for filtering material 

 which should have a certain affinity for the 

 liquid metal to be purified, without combining 

 with it. As iron possesses a strong affinity for 

 tin, without chemical combination, it seemed 

 a most suitable material for the purpose. He, 

 therefore, used leaves or sheets of white iron, 

 very thin, measuring about 60 millimetres by 

 4 millimetres ; 500 of these sheets were then 

 driven tightly into an iron frame, by means of 

 two wedges, and this frame was then fixed in 

 the open bottom of a graphite crucible. These 

 leaves would then form an effective filter, the 

 liquid tin being able, by virtue of its affinity, 

 to penetrate between the thin sheets, but the 

 smallest crystal of foreign metals would be ex- 

 cluded. 



The tin which was to be filtered was melted 

 first in another crucible, and was allowed to 

 cool until a thin coating of crystals had formed 

 on the surface. After skimming back this 

 skin, the liquid metal already becoming thick 

 was poured into the filtering crucible. The 

 liquid metal then percolated slowly through 

 the capillary interstices of the plates, leaving 

 behind a thick deposit, in which were found 

 iron, arsenic, and copper, concentrated to a 

 high degree, and mixed with a little tin. The 

 metal which had filtered through was almost 

 chemically pure tin. In this way as much as 

 twenty-five quintals of Bohemian tin were per- 

 fectly purified in an exceedingly simple and 

 inexpensive manner. Instead of the filter de- 



scribed as above, a mass of wrought or cast 

 iron shavings, or the borings submitted to a 

 high pressure in the bottom of a cylindrical 

 vessel, might be employed. 



Spectra of Metallic Solutions. -Messrs. Dela- 

 chanal and Mermet have devised an apparatus 

 which they call a spectra-electric tube, for the 

 observation of the spectra of metallic solutions. 

 It consists of a capillary tube traversed by a 

 platinum wire, which moves in it with sufficient 

 freedom to allow the liquid to flow through 

 drop by drop. The capillary tube, surmounted 

 by a reservoir containing the solution for ex- 

 amination, passes through the cork of a second 

 larger tube, placed immediately below it. 

 Through the bottom of this latter passes the 

 second platinum wire, the extremity of which 

 is brought within a short distance of the ex- 

 tremity of the upper one, while the liquid drops 

 between the two. The advantages claimed for 

 this arrangement are that the spark has a fixed 

 direction, and permits the prolonged observa- 

 tion of constant spectra ; and, secondly, that 

 the electrodes are inclosed in a tube, and the 

 spectroscope thus secured from chance of dam- 

 age. Finally, by a special arrangement, the 

 liquid employed is collected as it drops. 



Bronzes Incrustes. This is the name given 

 to a new style of bronze or copper work, orna- 

 mented with gold and silver, the manufacture 

 of a Paris firm. The ornamentation is pro- 

 duced by etching and electro-plating, and con- 

 sists, according to Dr. Meidinger, in the follow- 

 ing operations : After the object, which may 

 be of massive copper or bronze, has received 

 the desired form, the drawings are made with 

 water-colors, the body of which is white-lead. 

 If several pieces are to have the same design, 

 it may be printed on as in porcelain and/a^wce 

 painting. Those portions of the surface not 

 painted are colored with varnish. The article 

 is then placed in dilute nitric acid, whereby 

 the paint is dissolved and the surface of the 

 metal is etched to a certain depth. When the 

 etching is finished the article is washed with 

 water, and immediately placed in a silver or 

 gold bath, and a layer of the precious metal 

 deposited by electricity on the exposed por- 

 tions. When the latter operation is finished 

 the varnish is perfectly removed, and the whole 

 surface ground or polished, so that the orna- 

 mented portion is just even with the remainder 

 of the surface. The contours are quite sharp. 

 The surface is then bronzed, which does not 

 change the color of the gold or silver. A spe- 

 cially fine effect is obtained by producing a 

 black bronze of sulphuret of copper on por- 

 tions of the surface between the silver orna- 

 ments. A copper vessel then has three colors, 

 black and white drawings on a red-brown 

 ground of suboxide of copper. The produc- 

 tion of an incrustation requires a high degree 

 of manual skill and patience, but no costly 

 machinery ; indeed, every brass foundery con- 

 tains all the necessary tools for the mechanical 

 operations. 



