INDUSTRIAL AND ENGINEERING CHEMISTRY
164
centage abundance where the line is straight. If now the straight portion is extended through the smaller percentage range, the amount of the departure of the curve from the straight line gives a measure of the amount of the element present in the original materials. Thus, a correction can be made for residual impurities and applied throughout the range of the working curves. This procedure was followed in determining the working curves for all the test elements. TABLE I. Impurity SI01
Fe&s A1203
Ca 0
AIR0 A-1
cu
Xl n
Cr
COXP.4RATIVE
Spectrographic 70
Literature Cited Chemical I1
%
%
0 050
0 0 0 0 0 0 0
0.054 0,0003 0.012 0.0003 0.0005
0004 0106 0011 0005s 00004 000155 000054
None
N o trace
The method of analysis described above has been repeatedly tested for uniformity and acciiracy of results. Repeat analyses of the same specimen show a deviation from the mean of not more than 5 per cent of the amount presentwithin the deviation that might be caused by errors in measuring the densities of the spectral lines on the photographic plate and by the nonunifornlity of the plate. Check analyses of different specimens were made by chemical methods. In Table I the results of the spectrographic method are compared with those of two independent chemical analyses made by analysts in different laboratories. The widest yariations are for those elements which are most difficult t o determine by chemical methods. TABLE 11. Impurity
A. a3 Ah08 Ca BS CaO
A1
h l g as MgO
Si as Si02
Cr
cu Fe Mn
Ni Pb Sr
SPECTROGRAPHIC d X A L Y S I S
Spectral Lines Impurity M 3092 4226 2795 2881 2835 3247 3020 2798 3414 2833 4077
’
O
Range of Analysls 25% Caustic I.iquid
A. 3158 3903 2816 3158 3158 3158 3188 2816 3158 2816 3903
termined in this way when present in amounts down to 0.1 mg. per liter. The same spectroscopic source has been successfully applied in the analysis of steels and other metallic alloys. Glass, carbon, and graphite products have been analyzed for metallic elements by modifications of this method, using the type of source described. Experience indicates that this source and general procedure are capable of extremely wide application.
RESULTS
Chemical I
% 0 0 0 0
0
0
0
0 0
0 0
VOL. 10, NO. 3
70
0001 - 0.014 000054 - 0 005 00005 - 0 036 001 0 10 00002 - 0 010 000010 - 0 005 00001 - 0 010 000002 - 0 00052 000075 - 0 010 00002 - 0 0034 00001 - 0 010
-
The spectral lines used for the determination of the several elements, those of the control element, and the ranges of percentage abundance for which working curves have been plotted are given in Table 11. Experiments indicate that it should be possible by modifications of the spectroscopic source to extend the ranges of analysis to still lower values, as well as to high values. The spectrograph employed was a quartz instrument of medium dispersion giving a ospectrum 20 cm. (8 inches) long for the range 7500 to 2100 A. Eastman polychrome plates were used. A metal step diaphragm (4) was used for producing the calibration patterns on the plates and a clear glass gas-filled 250-watt tungsten lamp was found satisfactory as continuous source for the production of these patterns. Applications The method described for caustic liquors has been used successfully for determining traces of impurities-nickel and chromium plating solutions, various inorganic and pharmaceutical chemicals, and plastics. Urine and saliva have been analyzed for sodium, potassium, calcium, and magnesium by a similar procedure @),and the technic has recently been perfected for determining lead in urine, beverages, and other liquids, as well as organic tissues. Lead can be de-
(1) Duffendack a n d T h o m s o n , PTOC. Am. SOC.Testing Jfuteriuls, 36, Part I1 (1936). (2) Duffendack, Wolfe, and S m i t h , ISD. ENG.CHEM.,Anal. Ed.. 5 , 226-9 (1933). (3) Gerlach, W., 2. anorg. allgem. Chem., 142, 389 (1925); Gerlach and Schweiceer, “Chemische Emissionsspektralanalyse,” Leipeig, Leopold VOSS,1930. (4) T h o m s o n a n d Duffendack, S. Optical SOC.Am., 23, 101-4 (1933). RECEIVEDDecember 7 , 1937. Presented before the Division of Physical and Inorganic Chemistry, Symposium on Quantitative Spectrographic Analysis, a t the 94th Meeting of the American Chemical Society, Rochester, N. Y.. September 6 to 10. 1037.
Melting Point Determinations under Mercury JlYRON A. COLER Paragon Paint & Varnish Corp., Long Island City, N. Y.
T
HE relative inertness and high density of liquid mercury have been ingeniously employed t o determine the melting points of resins and waxes (8). The solid is fixed below the surface of the mercury either by melting the material and then allowing it t o solidify on the walls of a glass tube or by packing the finely ground solid into a capillary; heat is applied and the temperature a t which the material rises to the surface of the mercury or the mercury falls through the bottom of an open tube is noted. Since many resins are thermoreactive, premelting of the resins may change their melting points (1). The operation of stuffing such materials as soft waxes into capillary tubes may become tedious. Moreover, these methods do not seem t o take full advantage of the fairly high thermal conductivity of mercury. The method proposed here consists essentially of affixing a small piece of the original solid t o the bulb of a thermometer by means of a piece of wire. The thermometer bulb is then
-
50 CC.
BEAKER
MEACURY SAMPL P
W/R€ HOLDER
FOR MELTINQ POINT FIGURE 1. ARRANGEMENT DETERMINATION
MAEiCH 15, 1938
ANALYTICAL EDITION
submerged in a relatively large volume of mercury contained in a small beaker, so that the solid is completely surrounded by mercury except where it is held by the wire. The beaker is heated directly, so that the mercury serves as the bath medium. A good sample size is about 0.1 cc. The wire holder should be of a material not forming an amalgam. The heating rate should be approximately 5’ C. per minute. A suitable arrangement is indicated in Figure 1. Since there is a rather large exposed surface of hot mercury, it is essential that the work be carried out under a hood or that other means be provided for protection against the mercury vapor.
165
Satisfactory results have been obtained for a number of substances, including carnauba wax, candelilla wax, Glyco Wax A, and benzoic acid. The method requires very small samples, is rapid, and is practically foolproof.
Literature Cited (1) Eaton, J. RheoZ., 2, 392 (1931). (2) Gardner, “Physical and Chemical Examination of Paints, Varnishes, Lacquers and Colors,” 7th ed., p. 83i, Waahington, Institute of Paint and Varnish Research, 1935. RECEIVED February 5 , 1938.
Photoelectric RelayJ Unit GEORGE W. JOSTEN Pasadena Junior College, Pasadena, Calif.
F
OR some time it has been h o r n that liquids of sufficient opacity reduce the current in a photoelectric cell n-hen cutting off the light entering the cell, and dyes, suspended materials, or small floats have been added t o trans-
-8
3 -
I-
R4
FIGURE1
parent liquids to reduce the light to the “electric eye.” However, a meniscus acts like an opaque place in a liquid column for a limited distance. This limited distance of opacity is a t that point in the curvature of the liquid surface where total reflection takes place when light LAMP strikes a t an angle exceeding the critical angle. It can be made to cut off the light passed through a slit 0.5 cm. wide and 2 cm. long. In Figure 1 rays of light 4 and 5 would fail to get through the liquid meniscus if their angles of incidence exceeded the angle of total reflection of the liquid in the container. Rays 6 and 7 would be modified in direction.
=@
K i t h suitable slits on both sides of the container in line with the photoelectric cell and light source, a passing meniscus would cut off the light entirely, reduce the photoelectric current and cause the operation of the relay. After the meniscushas passed, the relay may return to its original setting. Although the current in the photoelectric cell may be different with liquid in place of air in the light beam, the relay circuit can be regulated with liquid in the beam beforehand by adjuding the potentiometer provided with the unit. In Figure 2, the light beam passing through the empty part of the cylinder keeps the relay circuit open to the buzzer. When the meniscus interrupts this beam, the buzzer sounds, and stops sounding when it has passed. A water meniscus rising in a 100-ml. graduated cylinder operated the buzzer when passing the beam from a 50-watt lamp with the potentiometer set a t 233 ’. Meniscus action on a light beam to a photoelectric cell is used in a new device (U. S. Patent 1,953,716, the Distillograph) to record distillation data automatically. The volume of distillate is recorded by means of a photoelectric cell operated by the meniscus as it rises in the receiver, and a t the
G-M LABS. INC. PHOTOTUBE RELAY 1224
110 VOLTS
FIGURE2
same time temperatures from the stillhead are graphed a t the volumes desired. RECEIVED January 4, 1938.
