516 U . S . BUREAU OF STANDARDS NOTES. [J. F. I.

processes such as the concentration and smelting of ores and the like are not discussed but the term is limited to a consideration of those features of composition, generally resulting from special treatment during preparation, which appear to have a marked effect upon the physical properties of the metal. The occurrence of gases in metals may be cited as an example.

For metals and alloys which are to be used in the cast state, the conditions attending the melting and casting of such materials are of prime importance in determining the properties of such materials. For metals which are to be given further treatment subsequent to casting the conditions of melting of the metal must also receive due consideration.

The circular summarizes the conditions under which tests of a metallographic nature will be conducted by the Bureau of Stand- ards. Specific directions concerning shipping, sampling, etc., are given.

ZINC C Y A N I D E P L A T I N G S O L U T I O N S . 2

By Wil l iam Blum, F. J. Liscomb and C. M. Carson.

[ABSTRACT.]

ZINC plating or electrogalvanizing was extensively applied dur- ing the war because of the fact that zinc coatings furnish by far the best protection against corrosion of steel. Satisfactory zinc deposits can be secured from either sulphate or cyanide solutions but the latter possess the advantage of "throwing V the deposit better into deep depressions or upon the surface of irregularly shaped articles. The cyanide solutions were therefore given first consideration in this investigation. It is hoped later to extend this study to include the sulphate solutions.

It was found that satisfactory zinc cyanide plating solutions can be made by using zinc oxide to replace part or all of the zinc cyanide formerly employed for this purpose. In the analysis of such solutions zin.c may be determined by the customary methods. It was not found possible to obtain by the usual methods any reliable results for either " free cyanide " or " free alkali." It is possible, however, to make fairly accurate determinations of the

2 Technologic Paper No. I95.

Oct,,i92i.] U . S . BUREAU OF STANDARDS NOTES. 517

total cyanide content and total hydroxide content from which data the probable constitution of the solutions can be computed.

It was found that the following conditions yield satisfactory results in practice. A solution may be prepared according to the following formulas, in which the concentrations have been rounded off to convenient values :

Approx. normality g/L oz/gal

Zinc oxide i.o 45 6 Sodium cyanide 1.5 75 Io Sodium hydroxide -3 I5 2 or Zinc cyanide ~.o 65 8.7 Sodium cyanide .3 20 2. 7

Sodium hydroxide 1.5 60 8

It should be operated at temperatures below 4 °0 C. (14 °0 F.) in order to reduce the decomposition of the cyanides. Current den- sities up to 3 amp/sq, din. (28 amp/sq, ft.) may be employed upon smooth surfaces but for general work about 2 amp/sq, din. (19 amp/sq, ft.) is preferable. The presence of large amounts of carbonate causes rough or striated deposits. Carbonates should therefore be removed from the solution at intervals by precipitation with barium cyanide or hydroxide, or by cooling the solutions to low temperatures.

RESULTS OF SOME TESTS OF MANILA ROPE?

By A. H. Stang and L. R. Strickenberg.

[ABSTRACT.]

THE results of tests on manila rope discussed in this paper represent some of the data which have accumulated at the Bureau of Standards during the past few years.

Most of the specimens were submitted by various rope manu- facturers on purchase orders for" government departments. A fixed procedure was adopted by the laboratory for all rope tests.

The rope ranged in diameter from ~ to 4 ~ in. inc., and consisted of commercial three strand regular lay ropes. The breaking load, weight per linear foot, number of yarns and

Technologic Paper No. 398.