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VP, VS t h e variable junctions. R is a variable resistance for cutting down t h e current when t h e difference in temperature between two junctions was so great as t o cause deflections beyond t h e galvanometer scale. S is a circular twelve-point changing switch for connecting t h e galvanometer with t h e variable junctions VI, V2, V6.
FIG.5
A detail of this changing switch is shown in Figs. and 3. Fig. z is from above, Fig. 3 is a vertical section. The solid black portions are formed of bakelite. R1 and R2 are of copper. The leads from t h e variable junctions are connected a t t h e bottom of t h e outer ring of contacts. A copper wire csnnects t h e galvanometer with t h e inner ring. A copper pin inserted in any one of t h e holes connects t h e outer contact with t h e inner ring, t h u s completing t h e circuit through t h e particular junction connected with this contact. I n order t o avoid thermoelectric currents, t h e pins, contacts, and both rings, R1 and Rz, were all formed from t h e same piece of copper tubing. As a further precaution, t h e bakelite support and t h e copper rings were suspended in a constant temperature oilbath, 0. (With t h e degree of accuracy demanded by these experiments this precaution was later found t o be unnecessary.) C is a lead conduit through which t h e cable of wires from t h e thermocouples passes t o t h e switch. Fig. 4 shows t h e construction of t h e grid which supports t h e variable junctions. The grid is placed in t h e can through t h e opening before t h e cover is 2
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sealed a t t h e top, t h e lead cable 0 being passed down through a round hole which has been cut in t h e bottom of t h e can. By means of t h e litharge packing L, t h e leather washers L1 and LP, and t h e n u t 111, a steam-tight joint is made a t t h e bottom of t h e can. The constant junction is a t C. The grid G is made of lignum-vitae. The ideal wire passes from t h e cons t a n t junction C, through t h e litharge packing and along t h e back of t h e grid G, as shown by t h e dotted line. The copper wires C1, CZ, Ca, etc., pass through holes in t h e grid and form t h e variable junctions where they are soldered t o t h e ideal wire. The leads from t h e constant junction and from t h e variable junctions pass through t h e lead cable 0 and out through t h e side of t h e autoclave. T h e copper leads are insulated with asbestos covering. T h e entire cable of copper wires is further wound with a single layer of asbestos cord. As an example of t h e results obtained with this apparatus, we reproduce a graph, Fig. j , showing a set of readings from a can of navy beans. On this graph t h e heavy line is a reproduction of the tracing of t h e thermograph record of t h e autoclave temperature. The abscissae and ordinate scales represent respectively t h e time in minutes and t h e temperature in degrees Fahrenheit. T h e other curves on t h e graph represent readings from t h e various thermojunctions. The drawing in t h e upper right-hand corner is a schematic illustration showing t h e location of t h e respective thermojunctions. The temperature of t h e constant junction ( N o . j in t h e illustration) is measured by t h e bulb of t h e thermograph, A, and is represented graphically b y t h e heavy curve. In t h e experiment which this graph represents, t h e can was placed in t h e autoclave and steam was turned on. As will be seen, a constant autoclave temperature of 280’ F. was reached in 1 5 min. The can remained a t this temperature for 180 min., and then t h e pressure of t h e autoclave was released, t h e autoclave opened, and both t h e can and t h e bulb of t h e thermograph quickly immersed in water. PREVENTIVE MEDICINE AND HYGIENE HARVARD MBDICAL SCHOOL
DEPARTMENT OF
B o s r o ~ ,MASSACHUSETTS
LABORATORY AND PLANT COMPARATIVE TESTS OF PALAU AND RHOTANIUM WARE AS SUBSTJTUTES FOR PLATINUM LABORATORY UTENSILS’ Hy I, J GUREVICHAND E WICHERS Received February 14, 1919
The high cost and scarcity of platinuni have greatly stimulated, especially within t h e past few months, t h e production of “platinum substitutes” €or various purposes. Of those intended for use as chemical laboratory ware, no alloy of base metals tested by t h e Bureau of Standards has been found suitable. Two types of alloys of gold and palladium have been placed on t h e market and have come into more or less general 1
Published by permission of the Director of the Bureau of Standards
use. These are known as “palau” and “rhotanium.” Rhotanium ware is manufactured in several grades, with varying proportions of gold and palladium. A discussion of these alloys, together with tests made by Professor H. H. Willard, has been published by Dr. F. A. Fahrenwald.‘ il series of tests has been carried out a t this Bureau t o determine t h e suitability of these alloys as substitutes for platinum in laboratory ware. Four rhotanium crucibles, two of grade A and two of grade C, were submitted for test purposes by Dr. Fahrenwald. This Bureau had previously carried out tests on a palau crucible submitted b y t h e Pacific Platinum Works, 1
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T H E JOC'RNAL OF I N D C S T R I A L A N D ENGINEERING C H E M I S T R Y
of Los Angeles, Cal. The results of these tests have been published in various technical journals' and i n advertising circulars issued by dealers in laboratory apparatus. For comparison with t h e results obtained with t h e rhotanium ware, t h e same tests were made on an unused palau crucible, purchased in t h e open market, and on a slightly used crucible of platinum with itbout 0.6 per cent iridium, made by t h e U. S. Assay Office a t New York. Palau and rhotanium C have very nearly the appearance of pure palladium, being somewhat darker t h a n hammered platinum. Rhotanium A had a distinct bronze t i n t . The rhotanium C and palau crucibles were somewhat stiffer t h a n those of rhotanium A and platinum with 0.6 per cent iridium. The composition of t h e rhotanium and palau alloys is represented by t h e manufacturers t o be as follows: Gold Per cent
Palau, .... 80 Rhotanium A , , . . . , . , . . , . . . . . , 90 Rhotanium C . . . . . . . . , . . . . . . . , 70
.
Palladinm Per cent 20 10 30
The maximum capacity of t h e rhotanium crucibles was 1 I cc., t h a t of t h e palau and platinum crucibles 16 cc. each. The total surface area of each of the rhotanium crucibles was approximately 40 sq. cm. T h a t of t h e palau and platinum crucibles was about 48 sq. cm. each. The weights of the crucibles were as follows: Rhotanium Platinum Grams 12.2745
Palau Grams 12.4116
Rhotanium Rhotanium
A1
Az
Grams
Grams
7.9615
7.3306
Rhotanium
c1
cz
Grdms 6.3555
Grams 6.0084
The tests were bf two types, t h e aim being t o determine t h e resistance of the materials t o chemical re. agents and their behavior upon heating. BEHAVIOR TOWARD CHEMICAL REAGENTS
Throughout this series of tests precautions were -taken t o secure weighings accurate t o 0.05 mg. Except after t h e sodium carbonate fusion, t h e final weight of one test was taken as t h e initial weight of t h e succeeding test. I n this one exception, t h e crucibles were cleaned by scouring before testing further. I n t h e treatment with nitric, sulfuric, and hydrochloric acids, ferric: chloride solution, and in the sodium carbonate fusion, t h e platinum and palau crucibles were treated in separate vessels, while t h e two rhotanium A and t h e two rhotanium C crucibles were treated in a third and fourth ressel, respectively. I n t h e treatment with sodium hydroxide solution and t h e hydrofluoric acid, all the crucibles were treated together in one vessel. I n t h e fusions with sodiu,m hydroxide and potassium pyrosulfate each crucible was treated separately. Further details of procedure are given in the following paragraphs. The results are collected in Tables I and 11. H S D R O C H L O R I C ACID-The crucibles were immersed in the boiling acid for 4 hrs. At t h e beginning of t h e test the specific gravity of t h e acid was 1.18, and acid ,of t h i s concentration was added t o replace t h a t lost Chem. Abs., 11 ( 1 9 1 7 ) , 2163, 2 6 2 7 .
571
by evaporation. At the end of t h e test the acid had a specific gravity of about 1 . 1 . The four resulting solutions were all colored slightly yellow. NITRIC ACID (SP. GR. ~.$z)--The crucibles were immersed in the boiling acid for 31/2 hrs. Acid of specific gravity 1.42 was added from time t o time t o keep up the volume. All t h e solutions except t h a t from t h e platinum crucible were decidedly yellow and gave tests for palladium and gold. There was no change in the appearance of t h e crucibles. NITRIC ACID (SP. GR. r.z)-The crucibles were immersed for 4 hrs. in t h e boiling acid. The solutions were not noticeably colored. The specific gravity of t h e acid was found t o have increased from 1 . 2 t o 1.3. SULFURIC ACID (SP. GR. 1.84)-The crucibles were immersed in t h e cold acid. About I hr. was consumed in heating t h e acid t o boiling. It was then kept boiling for 3 hrs. I n t h e calculations t h e test period was considered as 31/2 hrs. The acid from t h e platinum crucible was distinctly yellow, and t h a t from t h e rhotanium C crucibles slightly yellow. HYDROFLUORIC ACID (48 P E R C E N T ) - A ~of ~ t h e crucibles were immersed in t h e acid contained in a platinum dish which was covered by another dish containing water t o serve as a condenser. The acid was boiled about 3 hrs. and was tinged slightly yellow a t t h e end of this time. F E R R I C C H L O R I D E SoLuTIoN-The crucibles were immersed for I hr. in a boiling solution containing I O per cent hydrated ferric chloride (FeC13.6HzO) and j per cent (by volume) of hydrochloric acid (sp. gr. 1.18). Water was occasionally added t o keep up t h e volume. N o change in t h e appearance oE t h e crucibles was noted. S O D I U M H Y D R O X I D E SOLUTION ( 2 0 P E R CENT)-A~~ the crucibles were immersed for 4 hrs. in t h e boiling solution contained in a large platinum dish. Water was added from time t o time to keep up t h e volume. S O D I U M H Y D R O X I D E FusIoN-Each of t h e 6 crucibles was immersed in t h e fused alkali (technical) contained in nickel crucibles. The nickel crucibles were kept a t a dull red heat (about 600' C.) for I hr., in an electric muffle furnace. Both t h e inner and outer surfaces of t h e platinum crucible were badly discolored and almost black in spots, but t h e other crucibles merely presented a dull appearance. The normal appearance of t h e platinum crucible was restored on ignition in a reducing flame. It is t o be noted t h a t t h e change in weight is positive for t h e platinum crucible, and negative for all the others. S O D I U M C A R B O X A T E FusIos-The procedure was t h e same as in t h e sodium hydroxide fusion except t h a t a temperature of about 1000' C. was maintained for I hr. The platinum crucible was badly discolored. The others were rendered dull in appearance, but were discolored only in spots. Ignition did not restore t h e normal appearance of t h e platinum crucible. All t h e crucibles showed a gain in weight. A second carbonate fusion was now carried out, but this time t h e crucibles were nearly filled with t h e fused carbonate and placed, uncovered, in the muffle furnace and heated a t about 1000' C. for I hr. The results were t h e same
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as before, the discoloration of the platinum crucible being especially pronounced a t the rim, above t h e surface of the melt. No note on t h e change of weight was made. After cleaning t h e platinum crucible i t was again filled with sodium carbonate, covered with a platinum lid, and t h e fusion this time carried out over a Tirrill burner, t h e crucible being completely enveloped b y t h e flame. No discoloration appeared in this case and the inner surface of t h e crucible was only very slightly stained. The change in weight was not recorded. As it is well known t h a t in ordinary sodium carbonate fusions over the burner or blast lamp, the platinum suffers no attack, it appears t h a t t h e discoloration noted before was due t o t h e peculiar conditions which obtained in heating t h e crucible in t h e muffle furnace. The greater dissociation of the sodium carbonate and free access of air may have been t h e chief factors. POTASSIUM PYROSULFATE zusIow-Each crucible was immersed in the fused salt contained in porcelain crucibles. These were kept a t a decided red heat (about 750' C.) for I hr. There was no change in t h e appearance of t h e crucibles. USE AS CATHODE-The crucibles were used as cathodes in an electrolysis of a solution containing 4 mg. copper, 0.02 cc. nitric acid (sp. gr. 1.42), and 0.03 cc. sulfuric acid (sp. gr. 1.84) per cc. of solution. The crucibles were nearly filled with this solution. Platinum rods were used as anodes. The copper was dissolved off in warm dilute nitric acid, There was no change in t h e weight of any of t h e crucibles. USE AS ANODE-The crucibles were nearly filled with dilute sulfuric acid (I : 8) b y volume. Spirals of copper wire served as cathodes. With all t h e crucibles except t h e platinum, t h e surface which acted as electrode was stained brown t o black. With low current density, this film did not scale off, but as t h e current was increased t h e film adhered less firmly. Very little, if any, of t h e metal passed into solution, b u t t h e brown film produced by t h e electrolysis was readily soluble in hydrochloric acid. TABLE I-OBSERVED
CHANQES I N WEIGHT OF THE S I X CRUCIBLES RHOTANIUM A RHOTANIUM C CruCruCruCrucible cible cible cible PLATINUMPALAU 1 2 1 2
Hydrochloric acid, sp. gr. 1.18 Nitric acid sp. gr. 1.42.. Nitricarid:sp.gr. 1.2.. S u l f u r i c a c i d , s ~ . z r .1.84 Hydrofluoric acid; 48 per cent . . . . . . . . . . . . . . . . Ferric chloride s o h , 10 per cent ............. Sodium hydroxide s o h , 20percent Sodiumhydroxidefusjon Sodium carbonate fusion Potassium pyrosulfate fusion ...............
.............
.
..........
0.40 0.00 0.05 23.10
0.80 14.65 0.75 0.95
0.45 12.10 1.80 0.15
0.40 11 .OS 1.65 0.20
0.45 12.05 0.70 0.70
0.40 12.75 0.65 0.80
0.25
0.30
0.10
0.15
0.25
0.20
2.40
34.00
29.10
26.90
27.25
25.45
$0.05 $0.35 $0.40 2.95
$0.10 7.45 $0.65 10.85
TABLS11-WEIGHT
0.05 0.05 2.15 1.40 $0.50 f 0 . 5 0 2.60
2.70
0.10 $0.05 6.35 5.85 $0.95 +0.60 28.30
CHANQSS CALCULATBD TO 100 SQ. CM. PER THE FOUR KINDS OF WARE RHOPLATTANlUM INUM PALAU A Hydrochloric acid, sp. gr. 1.18.. 0.2 0.4 0.25 Nitric acid, sp. gr. 1.42 0.0 8.7 8.25 Nitric acid, sp. gr. 1.2 0.05 0.4 1.1 Sulfuric acid, sp. gr. 1.84., 13.75 0.55 0.15 Hydrofluoric acid 48 per cent.. 0.15 0.2 0.1 Ferric chloride soin., 10 per cent. 5.0 70.8 70.0 Sodium hydroxide soh. 20 per cent.. $0.05 $0.05 0.05 Sodium hydroxide fusion.. +O. 75 15.5 4.45 Sodium carbonate fusion. 0.85 $ 1.35 $ 1.25 Potassium pyrosulfate fusion.. 6.15 22.60 6.65
.....
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19.20
HR. FOR RHOTANIUM
C 0.25 8.9 0.45 0.55 0.2 65.9 0.00 15.25 I .95 59.4
+
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The observed changes in weight of t h e 6 crucibles when treated with t h e various chemical reagents named are given in Table I. Table I1 shows these changes calculated t o I O O sq. cm. of surface per hr. Weights are given in milligrams. All changes of weight, except those indicated b y t h e plus (+) sign, are losses. I n Table I1 t h e two results for each grade of rhotanium are averaged. B E H A V I O R UPON HEATING
The crucibles after t h e chemical tests were cleaned as follows: The crucibles were immersed in cold chromic acid solution, washed in distilled water, then in cold 'IO per cent sodium hydroxide solution. They were once more washed in water, dried with a clean cloth, and ignited t o a dull red heat. The crucibles were next boiled for j min. in dilute (I : 4) hydrochloric acid, washed in distilled water, dried, ignited, and weighed after cooling in a desiccator for 30 min. To compare with previous observations on platinum crucibles,' t h e heating and treatment with dilute acid were carried out as follows: The loss in weight of t h e 6 crucibles due t o heating was determined in a graphite resistance furnace free from metal vapors.2 The two rhotanium C and t h e palau crucibles were heated a t 1 2 0 0 ~ C., while t h e rhotanium A crucibles were heated at 1100' C., owing t o t h e danger of melting them a t t h e higher temperature. For comparison, t h e platinum crucible was also heated a t t h e lower temperature. The melting ranges of t h e three alloys are as follow^:^ ALLOY MELTINGRANGE Rhotanium A (IO per cent Pd). 1225'-1275' C. Palau (20 per cent Pd). . . . . . . . . . . . . . . . . . . . 1350°-13800 C. Rhotauium C (30 per cent Pd). . . . . . . . . . . . . 1410°-14250 C.
............
.
The crucibles were weighed before and after heating and also after a subsequent immersion of j rnin. in boiling (I : 4) hydrochloric acid. The observed losses are enumerated in Table 111. Table I V gives t h e d a t a calculated t o I O O sq. cm. per hr. Both rhotanium A crucibles were badly blistered when taken out of t h e furnace after their first heating,. while one of them even showed partial fusion in o n e portion of t h e rim after t h e second heating. I n s p i t e of this the losses due t o heating at 1100' C. were surprisingly low, and were not only lower t h a n for theplatinum crucible containing 0.6 per cent iridium heated t o t h e same temperature, b u t also lower t h a n those of platinum crucibles4 heated at only 1000' C. for threeperiods of 4 hrs. each. These last-mentioned losses. were as follows: 0.8 per cent Ir.. 0.9 per cent I r . . 2.4 per cent Ir..
......... 0.204 mg. per hr. per 100 s q . cm. . . . . . . . . . 0.550 0.374 mg. per hr. per 100 sq. cm. ......... mg. per hr. per 100 sq. cm.
Tables I11 and IV contain also some results previously. published (Columns 4 and 5), and also results on pre-vious tests of a palau crucible. The results obtained. A Burgess and Sale, Bureau of Standards, Scie?tti$c Pager 254, and Burgess and Waltenberg. Bureau of Standards, Scienlilic Pager 2 8 0 . 1 This furnace a n d method of operation are described in the Bureau of' Standards, Scienfific Paper, 254. a Ruir, Z . anorg C h e m , 61 (1906), 391. 4 Burgess and Walteuberg, Bureau of Standards, ScienlCfic Paper 280.. 367.
June, 1919
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TABLE111-OBSERVED CHANGESIN WEIGHTON HEATINGAND SUBSEQUENT ACID TREATMENT -PLATINUM-Platinum with 0.6 -RHOTANIUMA0.6 2.4 -PALAW---RHOTANIUMCPer cent Crucible Crucihle Per cent Per cent Crucible Crucible Crucible Crucible CRUCIBLE Ir 1 2 Irl Ira ia 2 1 2 Temperature of heating, deg. C.. ................. 1100 1100 1100 1200 1200 1200 1200 1200 1200 Surface area of crucible sq. cm.. 48 40 40 99 79 78 48 40 40 Loss in weight after firit heating, mg.. 1.02 0.13 0.13 1.984 9.85 7.30 1.82 +0.29s 1.01 Loss in weight after first acid mg.. 0.10 0.06 0.09 0.16 1.80 0.03 0.20 0.87s 0.07 Loss in weight after second hhating mg.. 0.62 0.20s 0.15 2.18 8.60 3.32 1.23 . 1.77 2.98 Loss in weight after second acid, mk.. 0.15 0.13 0.04 0.09 0.68 0.13 0.18 0.02 0.02 Loss in weight after third heating, mg.. 2.14 4.65 Loss in weight after third aSid, mg.. 0.07 1.60 .... .... .... Total loss in weight on heating, mg.. 1.64 0.33 0.28 6.30 23.10 10.62 3.05 2.69 2.78 Total loss in weight on acid treatment, mg.. 0.25 0.19 0.13 0.32 4.08 0.16 0.38 0.89 0.09 1 Burgess and Sale Bureau of Standards ScientZfic Paper 264 304 Table 5. 2 Burgess and WalienbeF, Bureau of Stgndards, Scicnlij6 Pader, 280, 367, Table I. 8 Bureau of Standards, est No. 20129, Dec. 2, 1916. 4 Three 2-hr. heating periods. 6 The gain in weight may be discounted as all of the gain and more was lost on acid treatment, indicating t h a t some silica from the marquard lining of the furnace stuck t o the crucible. 6 It was noticed on the completion of the second heating period t h a t partial fusion had taken place in one portion of the rim.
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....
WEIGHT ON HEATINGAND SUBSEQUENT ACID TREATMENT CALCULATED TO 100 SQ. Car. PER HR. Platinum --PLATINUMwith 0.6 -RHOTANIUM A0.6 2.4 -PALAW-RHOTANIUM cCrucible Crucible Per cent Crucible Crucible Per cent Per cent Crucible Crucible 1 2 1 2 Irl Irz CRUCIBLE Ir 1’ 2 1100 1100 1200 1200 1200 1200 1200 1200 Temperature of heating, deg. C.. 1100 Lqss in weight per hr. per 100 sq. cm. after 1st heat0.08 0.08 1.004 3.12 2.33 0.94 f0.18K 0.63 ing, mg.. 0.53 Loss in weight per hr. of heating per 100 sq. cm. after 0.04 0.05 0.08 0.57 0.01 0.10 0.54s 0.04 1st acid, mg.. 0.05 Lqss in weight per hr. per 100 sq. cm. after 2nd heat0.138 1.05 0.64 1.86 1.09 0.09 1.10 2.73 ing,, mg.. 0.32 Loss in weight per hr. of heating per 100 sq. cm. after 0.08 0.03 0.05 0.19 0.04 0.09 0.01 0.01 2nd acid, mg.. 0.08 Loss in weight - Der - hr. Der 100 sa. cm. after 3rd heating, mg.. 1.08 1.47 Loss in weight per hr. of heating per 100 sq. cm. after .... 0.03 0.51 3rd acid, mg.. 0.43 0.10 0.09 1.07 Average loss due t o heating per hr. per 100 sq. cm.. ... 2.44 1.69 0.79 0.84 0.86 Average loss due t o acid treatment per hr. per 100 sq.cm 0.07 0.06 0.04 0.06 0.42 0.03 0.10 0.28 0.03 1, e , a s a , c , e , See footnotes of Table 111. TABLE IV-CR&NGES
IN
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....
on t h e two palau crucibles do not check very well, but the values for the crucible obtained on the open market are much better t h a n those of the previous test. SUMMARY AND CONCLUSIONS
These tests indicate t h a t rhotanium A ware is superior t o platinum ware both of high (2.4 per cent) and low (0.6 per cent) iridium content in respect t o its resistance t o loss on heating. The losses on treatment with acid, after heating, are about equal. Grade A ware compares favorably with platinum in resistance t o boiling hydrochloric and hydrofluoric acids, t o boiling 2 0 per cent sodium hydroxide, and t o fusion with sodium carbonate in a muffle, and with potassium pyrosulfate. It is superior t o platinum in resistance t o the action of boiling sulfuric acid, and inferior in its resistance towards boiling concentrated and dilute nitric acids, boiling I O per cent ferric chloride solution, and for fusions with sodium hydroxide. The only objection t h a t may be raised t o its use is the rather low melting point of t h e alloy, which makes i t impossible t o blast or strongly heat the ware without melting it. As far as resistance t o loss in weight on heating to 1200’ C. is concerned, rhotanium C and palau wares are about equal, if not slightly superior, t o platinum ware containing 0.6 per cent iridium. They are surely superior t o platinum ware containing 2.4 per cent iridium. This conclusion leaves out of consideration results obtained in December 1916, on a palau crucible submitted by the makers. Palaul and rhotanium C 1 The
action of both concentrated and dilute nitric acid on the second palau crucible was markedly greater than on the crucible tested in December 1916. T h e results then obtained for concentrated nitric acid were 0.25 mg. per hr. per 100 sq. cm., and for the dilute about 0.1 mg. per hr. per 100 sq. cm. N o explanation can be offered tot this discrepancy.
....
....
....
....
....
....
.... ....
behave towards reagents in about the same way a s rhotanium A, except t h a t they are not suitable for potassium pyrosulfate fusions and are inferior t o grade A for sodium hydroxide fusions. The only striking distinction between rhotanium C and palau is t h e latter’s slight superiority in the case of the potassium pyrosulfate fusions. Palau and both grades of rhotanium may all be used t o advantage in the electrolysis of chemical solutions, but only as cathodes. As anodes the alloys are worthless. The solubility of platinum is recognized and its elimination is provided for in exact methods of analysis. With the palau and rhotanium wares two metals, namely, gold and palladium, may pass into solution, requiring somewhat different treatment for their elimination. I t is believed t h a t in addition t o the tests performed upon the palladium-gold alloys, information as t o t h e behavior of these wares in actual service would be of great value. Unfortunately there is little knowledge of this kind a t our disposal. A number of users have remarked upon the solubility of palau ware in nitric acid. One has written t h a t he “melted a (palau) crucible by overheating, lost a crucible by alloying with a nichrome triangle,’ and lost others on account of cracking a€ter a few months’ service.” It is suggested t h a t any further available information of this nature, both favorable and unfavorable, be communicated t o the Bureau of Standards. BUREAUOF STANDARDS DEPARTMENT OF COMMERCE WASHINGTON, D. c. 1 It should be stated in this connection that while platinum is lesr readily attacked by nichrome than the gold-palladium alloys, the use of nichrome triangles with platinum mare is not t o be recommended.
