INDUSTRIAL A N D EA'GINEERING CHE$.fISTRY
July, 1927
829
T a b l e I--Assay of 14 K. W h i t e - G o l d Single Plate (Fineness, 577.3 parts per thousand (13.86 K.); weight of sample, 85 t o 100 mg.) Av. DEVIATION TIME DEVIATIONO F Av. OF NUMBER FROM FROM SIZE STRIPOF Av. TRUE OF REMARKS DETNS.RANGE OF DETNS. Av. FINENESSFINENESS FINENESS SOLN. SPECIMEN PING Pavts per Hours Parts per thousand thousand K. Parts per thousand Sq. cm.
...
44 47 334 306
...
THICKNESS OF STRIPPED ALLOY, 0.0027 INCH (0.065 MX.)
4 4 4 6 4
4
579.3'&584.5 580.6 t o 5 8 3 . 3 5 7 2 . 9 to 5 7 8 . 5 5 6 5 . 6 to 5 7 6 . 3
...
...
581.4 581.8 576.1 571.8
...
...
13:95 13.96 13,83 13.72
2.6 1.3 2.8 5.3
...
...
$4:1 f4.5 -1.2 -5.5
...
Scarcely attacked during immersion of 1150 hours Blackened surface rubbed off Blackened surface rubbed off X o t appreciably attacked during immersion of 990 hours
0.0007 INCH (0.018 MM.) 1.9 +3.3 0.6 $2.8 Blackened surface rubbed off
THICKNESS OF STRIPPED ALLOY,
B B
4.5 4.5
20 24
4 6
578.5 to582.2 5 7 9 . 4 to 5 8 0 . 6
580.6 580.1
13.93 13.92
T a b l e 11-Assay of 10 K. Yellow-Gold S i n g l e P l a t e (Fineness 416.9 parts per thousand (10.00 K.); weight of sample, 70 t o 100 mg.) Av. DEVIATION DEVIATION OF AV. NO. FROM FROM OF Av. TRUE DETNS. R A N G E O F DETNS. Av. FINENESS FINENESS FINENESS Parts p e r Paris per thousand thousand K. Parts per thousand T H I C K N E S S OF S T R I P P E D ALLOY. 0.0027 I N C H (0.068 .~ MM.) 4 423.5 to 423.9 423.6 10.17 0.2 f6.7 ~
SIZE
OF TIMEOF SOLN. SPECIMENS T R I P P I N G
Sg. cm.
Houvs 168 22 20 22 192 72 960
4 6 3 6 2 2
425.8 425.8 427.7 410.2 411.9 411.5
to 4 2 6 . 9 to 428.2 to 4 2 8 . 4 to 412.5 and 4 1 2 . 1 and 4 1 1 . 8
1 1 1
426.2 431.4 436.6 418.6 412.1 to 414.3 4 2 2 . 2 and 4 2 2 . 6
426.4 426.8 428.0 411.2 412.0 411.6
T H I C K N E S S O F S T R I P P E D ALLOY,
A
B
C
E
D
F
9 9 9 9 7.5-9 9
26 33/r 23/4 72 90-113 114
1 5
2
426.2 431.4 436.6 418.6 413.5 422.4
distinctly ammoniacal, t o which about 3 t o 5 cc. of a 3 per cent solution of hydrogen peroxide were added at intervals of 24 hours, used at room temperature (20-25 O C.). The total volume of the ammoniacal solution was about 100 cc. F-A solution containing 1 volume of a 20 per cent solution of ammonium chloride and 1 volume of ammoniyn hydroxide (sp. gr. 0.90) used at room temperature (20-25" C.).
The specimens were immersed in the stripping solutions until the base metal had dissolved. The ammoniacal solutions were contained in stoppered flasks. I n some experiments the stripped layers were washed thoroughly with distilled water, dipped in alcohol, and dried in a n air oven at about 150" C . I n other experiments the blackened surface was rubbed with the wet finger before treating as described above. This removed a portion of the black material which was loosely adherent. R e s u l t s of Experiments
The results of the determinations of gold are given in Tables I and 11. The average values of fineness found, when 14 K. whitegold single plate was stripped of base-metal alloy in solutions containing nitric acid, ranged from 3 to about 5 parts per thousand greater than the value of fineness obtained on a sample of the gold alloy removed by milling. The average values found when the same alloy was stripped in solutions containing ammonium hydroxide ranged from about 1 to 6 parts per thousand less than the "true value." The average values found when 10 K. yellow-gold single plate was stripped in solutions containing nitric acid ranged from about 7 to 11 parts per thousand greater than the value of the milled sample, for layers of gold alloy of 0.0027 inch (0.068 mm.) in thickness and from 9 to 20 parts per thousand for layers of 0.0005 inch (0.013 mm.) in thickness. The average values found when the same alloy was stripped in solutions containing ammonium hydroxide ranged from about 5 to 6 parts less than the value of the milled sample
IO.23 0.5 1.2 10.24 0.3 10.26 9.87 1.2 0.1 9.89 9.88 0.2 0.0008 I N C H (0.013 MM.) 10.23 10,35 ... 10.48 10.05 ... 9.92 1.1 10.13 0.2
...
...
t9.5 T9.9 +1;.1 --0.7 -4.9 -5.3
+9.3 f14.5 +19., f1.7 -3.4 i-5.5
REMARKS
Blackened Blackened Blackened Blackened Blackened
surface rubbed surface rubbed surface rubbed surface rubbed surface rubbed
off off off off off
Blackened surface rubbed off Blackened sur face rubbed off
for layers 0.0027 inch in thickness and from about 3 parts less to about 6 parts per thousand greater for layers of 0.0005 inch in thickness. This discrepancy quite probably is to be ascribed to the different effect of the two types of solutions a t the boundary region of the gold and base metal alloys. No direct experiments were made to determine the solvent action of the solutions on the gold alloys themselves, but there is no apparent evidence in the tables that this effect was significant. There was apparently no appreciable difference between the action of solutions containing nitric acid on 14 K. whitegold alloy layers of 0.0007 inch in thickness and layers four times this thickness. There was, however, a significant difference with corresponding layers of 10 K. yellow-gold alloy. Although only one solution was used at an elevated temperature, comparative results appear to indicate that such a solution gave higher values on the 10 K. yellow-gold alloy. The error obtained when the blackened surface of the gold alloy was freed from loosely adhering material did not appear to affect the results of analysis appreciably. The average result for those samples not treated in this manner was, howerer, slightly higher.
Calendar of Meetings American Chemical Society-74th Meeting, Detroit, Mich., September 5 t o 10, 1927. Institute of Chemistry-State College, Pa., July 4 t o 30, 1927. Division of Organic Chemistry-Second National Symposium on Organic Chemistry, Columbus, Ohio, December 29 t o 31, 1927. American Electrochemical Society-Fall Meeting in the form of an excursion through the Northwest, September 4 t o 20, 1927. CenEleventh Annual Exposition of Chemical Industries-Grand tral Palace, New York, N. Y.,September 26 t o October 1 , 1927.
