5 1 8 U . S . BUREAU OF STANDARDS NOTES. [J. F. I.

An important accomplishment in this work was the com- pletion of a series of tests of the physiological effect (erythema) produced by using measured amounts of spectrally pure ("monochromat ic") and of spectrally heterogeneous ultra- violet radiation. The object of the measurements was to test this radiometric filter method as a dosage meter.

The sources used for producing the erythemic reaction differed very widely in ultraviolet spectral energy distribution. These sources were: (a) the sun, in which there is practically no radiation of wave-lengths shorter than 290 millimicrons; (b) a low voltage, relatively high vapor pressure, mercury arc, in a quartz bulb, which has a group of intense emission lines extending from 248 to 313 millimicrons; and (c) a high voltage, low vapor pressure, mercury arc in a quartz tube, in which 93 to 96 per cent. of the radiation of wave-lengths less than and including 313 millimicrons is emitted by the resonance line at 254 millimicrons.

Exposures were made on two observers. The observed time of exposure, and the calculated time, based upon the energy measured with the balanced filter radiometer and the spectral erythemic response curve, were found in close agree- ment- - (wi th in 5 to 8 per cent. in the case of the sun and the high pressure mercury arc). From this it appears that the spectral erythemic response curve is fairly well determined and that the heterogeneous ultraviolet radiation from various sources can be measured with considerable precision by means of the balanced filter radiometer.

NEW S T A N D A R D SAMPLES N O W AVAILABLE.

The following new standard samples have recently been added to the list of Bureau of Standards standard samples.

The bureau issues at the present time some Ioo standard samples comprising analyzed irons, steels, ferroalloys, non- ferrous materials, ores, refractories, clays, etc., also pure chem- icals and materials suitable for calibrating calorimetric bombs, polarimeters, thermometers, pyrometers, and other instru- ments. A complete list of these standards, prices, and ship- ping directions are given in Supplement to Circular No. 25 , which can be obtained free on application to the bureau.

Oct., I93I.] U . S . BUREAU OF STANDARDS NOTES. 519

Sample No.

9 I 92 93 94

95 96 97 98 99

Ioo

I0I

Name.

Opal glass Low boron glass Pyrex glass Zinc base die casting

alloy. do do

Flint clay Plastic clay Soda feldspar Medium manganese

steel.

18-8 Chrome-nickel steel (KA2S).

Constituents Determined.

Complete analysis. B20~ Complete analysis.

do do do do do do •

C, Mn, P, S, Si, Cu, Ni, Cr, V, Mo.

C, Mn, P, S, Si, Cn, Ni, Cr, V, Mo.

Weight, Grams.

45 45 45

IOO IOO IOO 60 60 40

I5o

I50

Price.

$2 .O0 2.00 2 .OO

2.00 2.00 2.00 2.00 2.00 2.00

2.00

3.00

Orders for any of the above samples should be accom- panied by money order or check made payable to the "Bureau of Standards, Department of Commerce." Detailed certifi- cates of analysis are sent to the same destination as the sam- ples.

WEAR RESISTANCE OF CARBON STEELS.

One of the major factors which causes deterioration of metals in service is wear. The cost of worn-out parts, the labor of replacement, and the time lost while repairing machin- ery represent a tremendous economic loss.

The selection, on the basis of laboratory tests, of those metals or alloys which best resist wear is extremely difficult because of the many complex factors involved. A study was recently completed of one special phase of this work, and a report will be issued in the September number of the Bureau of Standards Journal of Research. Tests of the wear-resist- ance of plain carbon steel were made in the Amsler machine (combined rolling and sliding friction under heavy pressures) to determine the effect of carbon content and heat t reatment upon the wear-resistance of these particular steels. The results showed that the higher-carbon and the harder steels were more resistant to the particular type of wear studied than the lower-carbon and the softer steels.