The Cu solution is added t o t h a t rico- t ~ r c ~!roiti ~ i tl.,c gold. by the next oper:;ti:m C O P 1’ E K .
Burn off the sulphides (,I g‘ It1 porcelain crucible, avoiding a heat gredtcr th:t t i t h a t required t o burn off the filter paper. Thi: hinders the shrinkage of the metallic gold, and leaves it more porous so t h a t the CuO is readily dissolved out. Too high a heat causes CuO t o unite with the glaze of the crucible. Place the Au and CuO mixture in a 4-ounce beaker. Add I O cc. of concentrated HSO,. Boil for I O minutes, Add 3 cc. of concentrated H,SO, and boil until the HNO, is all expelled, and SO, fumes are corning off freely. Cool, add 5 0 cc. of water and 5 grams of sodium acetate; boil and filter off the gold (the gold residues are weighed as an approximate check and are saved for their commercial value only. Gold is best determined b y fire assay). Cool the filtrate and add j grams of potassium iodide. Stir until dissolved. Titrate with decinormal hyposulphite of sodium: I cc. = 0.0063 gram Cu. GOLD.
Scorify 0.5 gram of filings with 40 grams of test lead. I gram of borax glass and I gram of powdered silica, The borax and silica flux are placed on the mixture of alloy filings and test lead. If the lead button resulting from scorification is hard, repeat the scorification, adding I O grams more test lead and z grams of borax and silica flux. Cupel carefully and weigh Au plus Ag. The determinations previously made make it possible t o calculate quite closely the amounts of Au and Ag, etc., in the alloy. We make up a mixture containing the same metals in approximately the same proportions. 0 . j gram of this “control” mixture is then scorified and cupelled side b y side with an equal weight of the allo?. After weighing the gold and silver buttons from the assay and the “control,” they are alloyed separately with three parts of pure Ag. The alloys must be thoroughly melted in order t o insure homogeneity. Flatten the buttons b y hammering or rolling. Part with H K O , of graded strengths as is the usual assaying practice. Boil well with water, dry, ignite and weigh Au. Deduct Au from Au plus Ag. The difference is Ag. Increase both Au and Ag figures b y the amounts of loss shown b y the Au and Ag used in the “control” assay. The fire-assay for Au and Ag yields in most chemists’ hands the highest and the most accurate results. The correction for fire loss (volatilization) is far higher for Ag t h a n for Au. Gold alloys analyzed b y us had the following limits of composition. Per cent. Gold.. . . . . . . . . . . . 4 8 . 0 t o 99.50 Silver. . . . . . . . . . . . 0 . 5 t o 26 00 Copper.. . . . . . . . . . 0 . O t o 18 . O O Zinc.. . . . . . . . . . . . 0 . 0 to 7.50 Tin . . . . . . . . . . . . . . 0 . 0 t o 2.00
Those alloys highest in Ag were most difficult t o dissolve in aqua regia.
We found the ratio 1 I-INO, to 4 HCl most efficient. . 4 q m regia I t o 3 w i ~ iless c:fficient and I t o 2 very unsatisfactory. Incr6,:i;ing the percentage of HNO, in the mixture failcd t o c:tuse more rapid solution, but increase of HCI produced unexpectedly rapid and complete decorxposition. PITTSBURGH TESTIXG LABOYATORY PITTSBURGH
CUPELL ATION. B y RAYMONI C. I 3 E N S E R AND JIIh’ER L. Received September 7 . 1911.
HARTMANN
I n the last few years there have been so many kinds of cupels proposed and placed on the market t h a t i t seemed desirable t o determine the relative value of some of the best known, regarding silver loss, conditions of surface, etc.. after cupellation. These observations suggested the investigation of the properties of substances other than bone ash, for separating lead and silver in the process of cupellation. I n order t o obtain uniform and comparative conditions an electrically heated muffle was used for all cupellations in this investigation. The temperature was determined by means of a Le Chatelier platinum iridium pyrometer.. Two cupels were run side b y side and the pyrometer placed between them about 1 / 4 inch above the tops of the cupels. The muffle used was just wide enough t o take two cupels and allow room for moving them about. The back part of t h e furnace was always hot enough t o “open” t h e buttons and t o start them ((driving,”after which they were pulled forward near the door of the muffle. After thorough drying, the cupels were heated in the muffle, a t about 800’C. The lead button was dropped into the cupel and the muffle door closed until the lead had melted down and begun t o oxidize. The cupels were then pulled t o the front of the muffle where the pyrometer registered about 665’ C. and continually watched. If any signs were discovered of more litharge being formed than was absorbed, the cupel was pushed back a little. It was found sufficient in many such cases to merely turn the cupel around, so t h a t the colder side would be facing the hotter part of the furnace. When the button had become quite small, seemed t o be revolving, and would “bliek” in from z to 3 minutes, the cupel was pushed back into the furnace where the temperature was from 750’ C. t o 800’ C. This was found necessary on account of a small amount of lead being retained in the silver button if the cupellation were completed a t a lower temperature. The bone ash obtainable for making cupels varies so much in size and purity t h a t some standard was necessary, with which t o compare the cupels tested. One was selected which gave the following screen test: Per cent O n 60 mesh. . . . . . . . . . . . . . . . 0,007 O n 80 mesh. . . . . . . . . . . . . . . . 7.83 On 90 mesh. . . . . . . . . . . . . . . . 3 3 . 2 2 On 100 mesh. . . . . . . . . . . . . . . 8 . 5 8 On 120 mesh. . . . . . . . . . . . . . . 43.65 Through 120 mesh. . . . . . . . . . 6 72
0
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERI,VG C H E X I S T R Y .
806
This bone ash gave the following losses for silver: Lead. Grams.
Average.
Series of s i x . . . . . . . . . . . . 10 Series of s i x . . . . . . . . . . . . 10 Series of s i x . . . . . . . . . . . . 10
Silver. Mgs.
Silver loss Per cent.
35-40 35-40 3540
2.45 2.30 2.33
Average, 2 . 3 6
Among other brands of bone ash, tests have been made of the following in regard to silver loss: Lead. Grams. D. F. C. Co. X‘. . . . . . . . . D . F. C. Co. X X . . . . . . . . D. F. C. Co. XXX.. .... Braun’s AAA?. . . . . . . . . . Braun’s A A A A . . . . . . . . .
10 10 10 10 10
Silver lo55 Per cent.
Silver. Mgs. 3545 35-40 35-40 3540 35-45
.
No. in series.
Grams of lead.
6 6
10 10
blgs. of silver.
Silver loss. Vol matter. Lead absorbed. Per cent. Per cent. Per cent.
35-45 35-45
2.17 1 82
Average,
*
0.0 0 0
92.0
No. in series.
Grams of lead.
Mgs. of
silver.
Silver loss Per cent.
6 6
10 10
35-45 35-45
2 90 3.29
-
1’01 matter. I x a d absorbed Per cent Per cent 5.9
...
98 1
Averagd. 3 09
Bromnite cupels are very similar to casseite as regards physical properties. They are almost black in color. The surface is slightly pitted after using and the silver button has a tendency to flatten out a t the end of the cupellation. The losses are given below. series.
Grams of lead.
6 6
10 10
M g s . of silver. 35-45 35-45
Silver loss. Per cent. 2.95 2 83
Volatile matter. Per cent
Lead absorbed. Per cent.
7.1
97.5
..
~
Average, 2 . 8 9 Fire Clay Co., Denver, Colorado. T h e Braun Corporation, Los Angeles, California.
1 Denver
*
K O ,in series. 6 6
..
Grams of lead.
Zlgs. of
silver.
Silver loss. Per cent.
10 10
35-45 3545
3.51 3.25
Average, 3 . 3 8 One half cement and one-half bone ash. 10 10
G 6
35-45 35-45
3.05 2 85
__ Average. 2 . 9 5
The losses in cement cupels have been determined and compared with those in bone ash cupels by J . W. Merritt.1 He finds t h a t a t orange heat, when using I O mgs. of silver, 6.38 per cent. of the silver is lost in bone ash cupels and 6.64 per cent. in cement cupels; a t light cherry heat, 4.62 per cent. in bone ash and 4.91 per cent. in cement. The temperatures are not stated in degrees. T. P. Holt and N. C. Christenson* have made a study of cupels made from different brands of cement as well as mixtures of cement and bone ash. They give the following summary of their results: S I L V E R 1,OSSES AT V A R I O U S ’fE31PEKATCRES.
C . S . Portland Red Devil Port- Half cement and A\,erage tern cement land cement hn!f bone ash. I1one ash Degrees C? Per cent. Per cent. Per cent. Per cent. 915 925 945 965
1 .99
Casseite cupels are light gray and hard enough to be handled safely when cold b u t when heated they become soft and pulverulent. The surface is smooth before cupelling b u t becomes slightly pitted after cupellation. The losses are given below:
No in
Cement cupels are used, a t present, in some districts. This material affords a very cheap substitute for bone ash and answers fairly well for small amounts of silver. Mixtures of cement and bone ash give better results than neat cement. The cupels are very hard before heating and are sufficiently adherent afterwards t o be handled without danger of breaking. The surface is as smooth as a cupel of bone ash and the button is detached with equal ease. Cupels made of Atlas Brand Portland cement gave the following results :
2.4 2.4 2.6 2.4 2 5
The manufacturers state, “Practically 7 5 per cent. of D. F. C. Co.’s X grade will pass a screen apparatus of 0.0147 inch (approximately 40 mesh), the X X X grade 0.00675 inch (approximately 80 mesh), and the X X grade 0.0091 inch (approximately 60 mesh).” Braun’s AAAA grade is rated at 80 mesh, and the AAA grade a t 60 mesh. Silver losses in cupels, made as nearly alike as possible from t h e standard bone ash and the cupellation carried out under the same .conditions, vary as much as 0.2 per cent., and, consequently, the results are accurate only t o this degree. All of the following tests were made under the same conditions as given for bone ash cupels. Morganite cupels are very hard, both hot and cold, and do not crack. The surface is smooth and finetextured. They give the smallest silver. losses of any which have come t o our notice.
Nov., 1911
1.30 1.81 2.53 3 37
1.34 I .72 2 56 3 .42
1.21 1.54 2.42 3.05
1.26 1 70 2.42 2.96
These temperatures are the temperatures of the lead buttons, which are about 1 2 5 ’ C. hotter than the air just above the cupel. Magnesium oxide or calcined magnesite has been suggested for making cupels. Some difficulty was encountered in finding a suitable binder for the material. Various organic materials were tried which made adherent cupels until they were heated. when they became very pulverulent. Xx&es with Portland cement were used but the cupels became very fragile after heating. Silica was next tried as a binder. Gelatinous silica made from water glass and hydrochloric acid was mixed with the magnesium oxide and fairly hard cupels were made. After cupellation, however, deep cracks were found on the surface of the cupels where lead oxide had been absorbed. Cupels made with varying proportions of sand (60 and 80 mesh) and magnesium oxide were tried, with the results given below: 1
Mzning uiui Scir?itific Press. May 7 1910
* E ? w .Win. J..90, 560-1.
CondiPer Sand tion of I,ead cent. Per cent. cupel. Gins 10 80 20 coarse soft 80 20 coarse hard 10 10 80 20 fine soft hard 10 80 20 fine 10 S5 15 coarse soft 10 S5 15 coarse hard MgO.
85 85
15 fine 15 fine
soft hard
10
Silver
h'gs 35-45 35-45 35-45 35-45 3545 35-45 35-45 35-45
10
Silver loss Per cent. Surface. slightly cracked 2 5 2 6 siightly cracked deer, cracks 2.3 2.5 deep cracks badly pitted 3.2 2.2 badly pitted cracked 3.3 slightly cracked 2.5 badly cracked
and
None of the magnesium oxide cupels have properties either as t o loss of silver or as t o hardness after cupellation, which warrant the substitution of t h a t substance fclr other cupel material. SUMMARY.
Under similar conditions, with about I O grams of lead and 40 mgs. of silver, the average percentage losses in different cupels were as follows: Silver loss. Per cent. Morganite.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Casseite., . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rron-nlte.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bone ash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cement. . . . . . . . . . . . ? . . . . . . . . . . . . . . . . . . . . . 1:quaI parts cement and bone a s h . . . . . . . . . . .
1 99 3.09 2.89 2.36 3.38 2.95
I t was furthermore determined t h a t cupels made of different grades and sizes of bone ash give the same percentage loss of silver within the limits of experimental error. UNIVERSITY O F ARIZOA-A,
'rucs,JK
Heat of conduction flows through solids, its rate of transit depending on the heat-transferring properties of the solid, its density, its specific heat, and its thermometric conductivity. Heat of radiation passes through space between surfaces, its rate of transit depending on the nature and disposition of the surfaces between which it passes and not on the space itself, t h a t is, not on the nature of the gas or vapor filling t h a t space. This is not absolutely correct, as there is no gas which is completely diathermanous, t h a t is, which does not absorb radiant h e a t ; but for air, products of combustion, and most gases of common occurrence, the absorption of radiant heat is negligible over short distances. The fourth-power law of heat radiation was first advanced b y Stefan' who found it t o accord with the results of experimental researches of Dulong anrl Petit, de la Provostaye and Desains, and Draper and Tyndall. Boltzmann later demonstrated math,.matically from thermodynamic principles t h a t sut 11 a law should hold. A surface of A square feet a t a temperatur:. af Q1 degrees absolute (equals 0, degrees Fahrenheit plus 460.7) radiates R heat units2 t o another surface whose absolute temperature is @,, in a length of time T hours. The mean solid engle subtended b y the latter surface with respect t o the surtace in question is o hemispheres. The net coefficient of emission and absorption between two surfaces is E. According t o the Stefan-Boltzmann radiation law, the following relation exists:
HEAT RADIATION. nv HAROLDP GURNEY Received Aun 9. 1911
Heat transmission b y radiation is utilized in the abstraction of heat from the zone of combustion in furnaces, and it is the principal restrictive factor in the maintenance of high temperature. Chemical and metallurgical industries abound with instances where application of the well established laws of heat radiation and conduction would reveal important information with regard t o economy of operation or design. Although heat radiation is rarely unaccompanied b y conduction and convection of heat, i t may well be treated separately, a t first, as i t is subject t o different laws. The laws of heat radiation differ in very essential respects from the laws of heat conduction. Heat always flows from high t o low tem'perature, b u t the rate of flow of radiant heat is not proportional t o the temperature difference. When heat IS transmitted b y conduction, the thermal pressure causing the flow of heat may be considered as proportional t o the absolute temperature, consequently the rate of flow per unit of temperature drop IS a constant, because the differential of the thermal pressure with respect t o the temperature is a constant. The pressure of radiant heat is proportional t o the fourth power of the absolute temperature, consequently the rate of flow per unit of temperature drop a t a n y tempetature is proportional t o the cube of the absolute temperature
R
=
---4 ----41 o.16TAyE [o.oI@, -- o.o~@,,J
The constant in the above expression has been variously assigned t o values ranging from 0.136 t o 0.190.3 I t was originally given as o . r g z , b u t late work4 b y Bauer and Moulin places i t a t 0.160, and it has ordinarily been quoted a t 0.I 60. The coefficient of absorption of a surface is the ratio of the amount of radiant heat absorbed t o the amount of heat incident on the surface. Lampblack absorbs practically all heat rays impinging on its surface and reflects none; its coefficient of absorption, then, is unity. The coefficient of emission is the ratio of the heat actually radiated t o the heat an ideal black body would radiate, and i t is the same in value as the coefficient of absorption. The net coefficient between two surfaces is very nearly the product of the coefficients of both surfaces, as the heat transmitted will be diminished both in emission and in absorption. y is the mean of the solid angles subtended b y one surface with respect t o each elementary area of the other surface. A unit solid angle is bounded by a hemisphere and this is the most usual technical case. Rules cannot be given for evaluating y under all circumstances; but as this matter is seldom given b u t scant consideration, it will here be taken u p more in detail. 1 2
3 4
Wiener, B c r . , 1872. British thermal unit. C. Fer,., Compf. r e n d . . 1909. E. Bauer and A f . Moulin, Jouvnnl Physique, 1910.
d
