by the quinhydrone apparatus was never more than 0.1 pH different from that of the solution entering the flow thannel. Another important fact to be recognized in this connection is that in the majority of industrial installations an endeavor is made to maintain the pH value of a solution within narrow limits. I n such cases, the time lag becomes negligible.
L
Vol. 4, No. 2
ANALYTICAL EDITION
178
LITERATURE CITED (1) Coons, c. c.,IND. ENG.CEEM.,Anal. Ed.,3,402 (1931). (2) Greer, W. N., Canadian Chem. Met., 15,239 (1931). (3) Joos, C.E.,Combustion,3 (4),25 (1931). (4) Richardson, K.8 Chem. Met. EW.9 37,293 (1930). RECEIVBID November la, 1931.
Examination of Electrodeposited Metals and Alloys with X-Rays H. KERSTEN, University of Cincinnati, Cincinnati, Ohio
aT
HE methods of x-ray crystrll structure analysis may be
used for examining electrodeposited metals and alloys to determine their structure, approximate chemical composition, approximate thickness, and relative grain size.
FIQURE 1. X-RAYCAMERAFOR EXAMININQ ELECTRODEPOSITED METALS The theory of the methods has been described in several books on the subject @,S, 6,9,IO) and need not be repeated here. The special apparatus required is illustrated in Figure 1 where the x-rays from a slit at B strike the sample clamped in such a way a t D that its surface is on a diameter of the hoop A . The x-rays strike the sample at the
I
taken with the radiation from a special gas-type x-ray tube (6)having an iron iarge-t; operated a t 50 milliamperes and 20,000 volts. At this voltage and current each picture required an exposure of onehalf hour. All the photographs shown are full size, but much of the detail observable in the original negatives cannot be seen in the printed pictures. The strong white line which can be seen a t the left of each picture was made by the main beam comh g from the slit before the sample was clamped in place. If an object is electroplated with an alloy solely to give it a desired color, as is usually the case, a comparison of colors is the onlv examination needed to determine whether.& deposit is satisfactory. I n the cases of alloys which have a constant
l I
color for a wide range of compositions, it is sometimes possible to determine their composition with a sufficient degree of accuracy by means of the methods of crystal structure analysis without stripping the deposit or damaging the electroplated object in any way. With this method it is the crystal structure of the surface layer and not its color of chemical composition which is examined. The relation between structure and chemical composition for many alloys has been investigated. A collection of these results has been published in two volumes by Neuburger (7, 8). Figure 2 shows photographs of zinc, two kinds of brass, and copper taken with the camera described above. A comparison of these with those given by Westgren and Pragmen (11) indicates that one of the brasses belongs to the alpha phase and the other to the alpha-plus-beta phase. These samples were plated from baths having the following compositions: ALPHA (1): Copper cyanide (CuCN), grama.. Zinc cyanide Zn CN I) grama... Sodium cyani6e (hadN\ grama.. Sodium oarbonate (NazCbs), grama.. Water, liter Current density, 0 . 6 ampJdrn.2 Temperature, 23O C.
............. 27 ............. 9 ............. 54 .......... 30 ................................. 1
FIQIJRE 2. ELECTROPLATED BRASS.Top, zinc; upper center, alpha brass; lower center, alpha-plus-beta brass; bottom, copper
I
April 15, 1932
INDqSTRIAL AND ENGINEERING CHEMISTRY
ALPHAPLUS BHITA: Copper cyanide (CuCN), grams.. ........ Zinc cyanide (Zn(CN z), grams.. ......... Sodium cyanide (NadN ........ Sodium carbonate (Nandbf;:Ems. Water, liter.. Current density, 3 amp./dm.z Temperature, 6 3 O C.
................................
179
15 30 75 30 1
Since the alpha phase of brass may contain from 0 to 36 per cent of zinc, and since the x-ray p h o t o g r a p h s for this phase do not change appreciably with composition, the x-ray examination does not give very precise information as to composition. The p h a s e c o n t a i n i n g alpha and beta crystals, lion-ever, contains from 36 to 45 per cent zinc, so that the determination of the coniposition is more exact but much less so than a determination by chemical analysis. Another illustration of the method is given in the Of copper by FIGURE 3. TIN AND COPPER. Top, tin; middle, tin-copper alloy formed by “immersion.” A piece of tinfoil dipped immersion; bottom, copper in a solution of copper sulfate is apparThe radiation from x-ray tubes having targets of high atomic ently coated with copper in a few seconds, The x-ray photographs show a t once that the copper has alloyed with the tin, number penetrates the material which it strikes more deeply for (Figure 3) thelinesappearing are neither those of tin nor than that from tubes having targets of low atomic number. those of copper alone, and are not entirely a super-position of With a given target, the depth to which the radiation peneboth sets of lines on one photograph. Cobalt is k n o m to crystallize in both the hexagonal close-packed and the cubic face-centered systems (4). E l e c t r o \ deposired cobalt usually consists of a mixture of both systems, the relative proportions possibly depending on the conditions under which i t is deposited. ..__ Figure 4 shows the pictures for tnFo sam@ ‘i ples of electrodeposited cobalt, one of I which is plated from a saturated solution of cobalt formate and the other from a solution of the same composition ex‘.%e ceut that the aciditv was changed bv ” adding a small amouit of ammonium hyFIGURE 4. COBALT.Top, from saturated cobalt formate; bottom, less acid solution droxide. The temperature and current density in each case were 23” C. and 0.5 amp./dme2,respec- trates depends on the voltage a t which the tube is operated tively. Possibly because of the two crystal systems present, and on the atomic numbers of the elements through which it or for reasons unknown, cobalt does not give good diffraction passes. This fact makes it possible to use the methods of lines, so that the photographs are not so sharp as others. crystal structure analvsis for the relative determination of the t h i c k n e s s of electrodeposited metals, when the base metal has a structure A sufficiently different from that electrodeposited to permit two sets of lines being distinguished on the films. Figure 5 shows how this method may be applied. The u p p e r picture is of silicon steel. The middle picture was taken of the same sample after it had been given a “flash” of cadmium too thin to be measured with the ordinary micrometer. The strong speckled line of iron a t A still shows through the cadmium. The lower picture is the same sample after having been plated with a coating of cadmium 0.015 mm. thick. The speckled line of iron is nearlyabsent. When determining thicknesses by this method it is necessary to operate the x-ray tube at the same voltage and the same length of time, using the same kind of x-ray films in order to get oomFIGURE 5. SILICON STEEL.To-p, silicon steel; middle, with flash of cadmium; parable results. If these conditions are bottom, with 0.015 rnm. of cadmium
I I
.
1
1
ANALYTICAL EDITION
180
VOl. 4, No. 2
deposition, a thick deposit does not necessarily have the same s t r u c t u r e throughout. This is illustrated in Fig-
FIGURE 6. COPPER. Top, coarse-grained; bottom, fine-gained
and 3 amp./dm.2 on -stainless steel to which it did not adhere well, and could be strimed. It was 0.35 mm. thick. The toD-iart of Figure 7 is a Dicture of the the structure of the part lastdeposited. The lines in the lower picture show a shift toward the left, a characteristic of the alpha phase as the percentage of
’ Hill, 1927.(3) Glocker, “Materialpruefung mit Roentgenstrahlen,” Springer, 1927. (4) Hull, Phw. Rev., Dl 17, 576 (1921). ( 5 ) Kerstenv Rev. SCi. Instruments,3, 145 (1932). Marc, “Die Verwendung der Roentgenstrahlen in Chemie und Technik,” Barth, 1926. (7) Neuburger, “Roentgenographie des Eisens und seiner Legierungen,” Enke, 1928. (8) Neuburger, "Roentgenographic der M e t a h und ihrer Le&ungen,” Enke, 1929. (9) . , Schleede and Schneider, “Roentaens~ektroskopieund Kristallstrukturanalvse.” deGruvter. 1929.(10) Trillat, “Les hplications des Rayons X,” Les Presses Universitaires de France, 1930. (1925), Westgren and Pragmen, Phil. Mag., [61
FIGURE 7. BRASS. Top, next to cathode; bottom, away from cathode fixed, then a photograph of a sample plated with a coating of unknomin thickness may be compared with a set of those carefully prepared from samples of known thickness to determine whether the deposit is thicker than required or not so thick. The photographs in Figure 5 also indicate that the x-ray examination itself only with the surface layer when the soft radiation from It target Of low atomic number is used. The relative grain size of electrodeposited metals may also be determined with the same camera. Figure 6 illustrates this for the case of copper electrodeposited from an ordinary acid copper sulfate bath. The top $cture shows the speckled
RECEIVED September 22, 1931.
Determination of Minute Amounts of Boron in Soils WILFRED
W.
SCOTT AND
SONDHEIM K. WEBB, University of Southern California, Los Angeles, Calif.
INUTE amounts of boron are essential to the normal development of such plants as the tomato, soy bean, tobacco, and others, but, on the other hand, as little as three to four parts per million by weight in the soil may have a decided toxic effect on other plants. Citrus and walnut trees are seriously affected and sometimes killed by very small amounts, hence the importance of a rapid and accurate method for the testing of soils is evident. Further reference to the effect of boron on the growth of plants will be given in a paper on the analysis of the irrigation waters of Southern California. Three representative types of methods for the determination of boron are Chapin’s modified volumetric method ( 6 , 5 ) , the gravimetric method as outlined by Gooch and Jones (S),
and the colorimetric method originated by Bertrand and Agulhon (1). Large samples of soil are necessary for the determination of small amounts of boron by either the volumetric or gravimetric methods, and not being nearly so rapid as the colorimetric method they are not recommended for the determination of minute quantities of boron in soils. The modification of the colorimetric method presented in this paper permits the determination of amounts of boron well within the limits that have an appreciable effect on plants. Tests with known amounts of boron as boron oxide, ranging from 0.005 to 1.Omg., gave fairly accurate quantitative results. The method is applicable to the determination of boron in soils, and satisfactory results may be obtained with samples of soil weighing 100 grams or less. The procedure for the
