May,
1920
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
PRACTICABILITY
O F THE N E W METHOD
The new method in its present form requires more time t h a n t h e A. L. C. A. method, b u t this disadvantage must be considered negligible compared t o t h e advantage of greatly increased accuracy. If t h e new method is t o prove satisfactory from t h e standpoint of setting a price on tanning materials, i t must give results which are readily reproducible in different laboratories. We are convinced t h a t i t will do this quite as well as t h e official method when t h e different analysts become used t o manipulating i t . The several results for any one material in Table I were determined days, a n d sometimes weeks, apart. The hide powder used in t h e new method is not chromed, b u t is used exactly as i t comes from t h e manufacturer. If, however, i t is first chromed, i t gives a higher result for Osage orange, apparently due t o t h e chrome acting as a mordant for t h e coloring matter. But this coloring matter does not precipitate gelatin nor does it form a stable compound with unchromed hide fiber and we feel t h a t t h e method is t h e more accurate for not estimating this coloring matter as tannin. The question of putting a value on this coloring matter may have t o be solved, b u t this problem will probably be confined t o very few materials. On t h e whole we believe t h e new method will be found quite as practicable a n d certainly very much more satisfactory from t h e standpoint of accuracy t h a n t h e present official method. What has been said concerning t h e A. L. C. A. method applies equally well t o t h e European methods since t h e y differ only in detail. SUMMARY
A new method of tannin analysis is described which we believe determines exactly what is called for in t h e generally accepted definition of tannin from a practical viewpoint, namely, t h a t portion of t h e water-soluble matter of certain vegetable materials which will precipitate gelatin from solution and which will form compounds with hide fiber which are resistant t o washing. The analyses of eight common tanning materials by t h e new method and by t h e official methodof t h e American Leather Chemists Association indicate t h a t t h e latter method is in error t o t h e extent of from 43 t o 2 2 0 per cent. T h e new method gives reproducible results and is considered entirely practicable. PRACTICAL METHODS FOR THE DETERMINATION OF RADIUM. 111-ALPHA-RAY METHOD, GAMMARAY METHOD, MISCELLANEOUS’
By S. C. Lind BUREAUOF
MINES EXPERIMBNT STATION, GOLDEN, COLORADO Received October 29, 1919
I n two previous papers2 t h e writer has described a form of interchangeable electroscope, t h e details of its construction, and its use in connection with t h e determination of radium by t h e emanation method.
I n t h e present paper, i t is proposed, first, t o discuss briefly some more recent modifications in t h e construction of t h e electroscope, which have contributed materially t o t h e ease and accuracy of its manipulation; second, t o discuss rather fully t h e application of t h e a-ray method t o t h e determination of radium in solids without reference t o any particular form of electroscope; and, third, t o consider briefly t h e y-ray method of determining radium. MODIFICATIONS
IN
THE
IXTERCHANGEABLE
ELECTRO-
SCOPE
Conditions due t o t h e European war necessitated an electroscope of American make. I n devising one, t h e writer had economy and accuracy equally in mind, and sought t o combine as far as possible in a single instrument t h e advantages of t h e various types already in use. The advantages sought have already been mentioned,’ b u t perhaps a somewhat fuller explanation in t h e way of acknowledgments will not be out of place. The “interchangeable” feature, enabling t h e use of a detachable head carrying t h e reading device and leaf system, was first used b y Professor Ebler,’ in connection, however, with t h e Exner type of doubleleaf electroscope. Instead of t h e latter, i t was desirable t o use t h e simpler single-leaf Wilson t y p e so modified t h a t t h e leaf could be readily removed if replacements were necessary. The highly advantageous feature of having t h e reading microscope firmly fixed t o t h e head so there can be no chance of accidentally changing t h e relative positions of leaf and micrometer scale of t h e microscope was adapted from t h e Wulf3 electrometer, thus providing rigidity while preserving complete visibility of t h e leaf system-an advantage not possessed by t h e Wulf instrument. The most far-reaching change in t h e instrument, since its earlier description, consists in t h e substitution of amber or amberoid insulation instead of sealingwax for both insulators (points g and d in t h e original) . 4 This substitution made it necessary, however, t o provide a new means of rendering t h e emanation chamber gastight. This has been accomplished without t h e use of any binding material by an ingenious arrangement, due t o Mr. P. F. Elzi, of t h e SachsLawlor Company, Denver. Fig. I illustrates its construction. The brass collar a is threaded into t h e lower chamber (not shown) a t b and made gastight by means of a lead washer, c. The collar a is hollow and provided with an interior projecting shoulder, d , on which rubber washers rest a t f a n d f’ above and below. On f and f ’rest amberoid discs, g and g’, pierced b y t h e rods h and h’, both of which are threaded into t h e connector i. The holes through g and g’ are made tight b y small rubber washers j and j’. h terminates above in a shoulder, k , resting on t h e washer j and a tip I t o make electrical contact with t h e spring s attached t o the leaf system above. Below, h’ is provided with a similar shoulder, k ’ , which rests 1
1 Published with permission of the Director of the U. S. Bureau of Mines. 2 THISJOURNAL, 7 (1915), 406, 1024.
46 9
2 8 4
Part I, LOC.cit. Chem. Kalendar, 1914, Part 11, 367. Physik. Z , 8 (1907). 246, 527. Part I , LOC c i f . Fig 3
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
4 70
on t h e washer j’ a n d l e a d s below t o t h e electrode e. By screwing h and h’ into t h e common connector i, tension is applied on t h e washers f and f’ and j a n d j’, t h u s giving gastightness t o the lower chamber without a n y binding material. This simple device has proved eminently satisfactory, usually holds gastight for a year or more, and can be readily tightened or, if necessary, taken a p a r t t o renew the washers. Much labor in recalibrating t h e instrument is avoided in this way. 5n
Vol.
12,
No. 5
This method, as practically applied t o radioactive ores, has been described by Moore and Kithill a n d briefly commented on by Parsons, Moore, Lind, a n d Schaefer.2 I t s refinement for scientific measurements, with reference t o the penetration of layers of various depths by a-rays, has been carefully worked out by McCoy.3 Owing t o its sensitiveness, simplicity, a n d ease of manipulation, this method has been more generally used t h a n any of t h e methods of measuring radioactivity. a - R a y instruments are now very generally used in prospecting, ore sorting and milling, and for certain purposes even in t h e control of r a d i u m plant operations. For qualitative and very roughly quantitative purposes the a-activity furnishes a quick and satisfactory method. Attempts t o extend its use for more quantitative purposes are beset with many pitfalls and uncertainties which are discussed in this paper, T o illustrate t h e fundamental difficulty in its use for quantitative purposes, complaint has been made t h a t the results of a - r a y activity measurements frequently do not check even roughly with other results, such as t h e determination of uranium b y chemical methods, or the direct determination of radium by t h e emanation method. These discrepancies have been especially marked for carnotite ores from different localities, as can be seen from Table I. TABLE I-SHOWINGTHE VARIABILITY OF DIFFERENTCARNOTITES IN RAY
ACTIVITY PER URANIUMCONTENT
FIG. 1-COLLAR
OF
W ELECTROSCOPE WITH AMBEROID INSULATORS MADE GASTIGHT WITHOUT C E M E N T
Further changes have consisted in replacing the two rubber-connected glass stopcocks with metal stopcocks brazed into the chamber. T h e microscope holder has also been made adjustable by means of a heavy milledhead screw (Fig. 2 ) . I n t h e new construction the front metal plate carrying the microscope fits into the head cylinder by means of a V-groove carrying three tightening screws, by loosening which t h e plate can be rotated t o bring t h e microscope t o view the leaf a t any desired part of its arc. T h e changes mentioned above have materially added t o t h e usefulness and accuracy of the interchangeable electroscope. THE
ALPHA-RAY
METHOD
O F ESTIMATING
RADIUM
Per U3Oa cent a-Activity SAM- (By (Arbitrary PLE Analysis) Units) 0.087 l . . . 1.52 0.064 2... 1.60 0.139 3 . . . 2.07 0.172 4 . . . 3.16 0.207 5 . . . 4.78 0.259 6 . . . 9.12 0.733 7 . . . 23.40 1.206 8... 33.20
or-Activity
a-Activity E m . power P e r cent U30a Per cent 0.0572 20.4 0.0400 50.5 0.0671 29.6 0.0544 39.7 0.0433 33.90 0.0284 30.4 0.0313 45.8 0.0363 16.2
Ra Per cent U 102.7 94.9 101.5 119.2 98.8 84.1 72.4 107.8
U30B
Corrected 0.0638 0.0582 0,0804 0.0631 0,0542 0.0382 0,0508 0.0381
I n Table I , the samples of carnotite represent all grades from a low t o a high percentage of USO8, a n d also come from various localities in Colorado a n d Utah.
IN
SOLIDS
I n its simplest form, this method consists in exposing a solid powder covering a plate of definite surface and depth in the discharge chamber of an electroscope, which might be of t h e t y p e illustrated by the middle chamber shown in Fig. 2. By comparing t h e rates of discharge of t h e leaf as viewed through a microscope provided with a micrometer scale, first using a solid with known uranium or radium content a n d later t h e unknown, a more or less approximate idea is obtained of t h e radium or uranium content of the latter.
FIG.2
If the a - r a y method, as usually applied, were really applicable t o all carnotites, then t h e ratio of surface activity t o t h e percentage of U308 given in t h e fourth U. S. Bureau of Mines, Bulletin 70 (1913), 64. Z I b i d . , 104 (1916), 87. 3 Phys. Rev., 1:(1913), 393. 1
May, 1 9 2 0
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
column should be constant. Evidently this is not even approximately true, and one can see a t once how f a r astray one might be led in choosing any of these different samples as standards for other a-ray comparisons. I n seeking t h e reason for these deviations, three principal causes present themselves: I-Variation in t h e amount of t h e loss of radium emanation b y gaseous diffusion from t h e ore; t h e percentage loss is usually referred t o as t h e “emanating power.” This entails t h e loss of a-radiation, not only from t h e emanation itself, b u t also from t h e succeeding a - r a y members, RaA, C, and F. The actual percentage loss for t h e ores under consideration is reported in t h e fifth column of Table I, and, as has already been pointed out by Lind and Whitternore,’ is not only unusually high for carnotite, but also quite variable. 2--A second possible source of error is t h e variability of t h e radium-uranium ratio in carnotite. As also reported by Lind and Whittemore,2 this variation is confined t o small specimens of carnotite which can vary considerably from the normal value of t h e radiumuranium ratio. This variation is reported in the sixth column of Table I in terms of per cent, placing t h e normal (pitchblende) ratio equal t o I O O per cent. I n t h e last column t h e values of Column 4 have been corrected according t o t h e d a t a in Columns 5 and 6 ; t h a t is, t h e discrepancies introduced by t h e variation of (x-radiation, due t o “emanating power” and abnormal ratio of radium t o uranium, have been eliminated. The improvement in t h e degree of constancy of activity compared with t h e uranium content can be seen t o be very slight. Evidently there must be another source of error more far-reaching in its influence t h a n either of t h e first two. 3--This source of error lies in t h e position of t h e radioactive material in t h e individual grains and also t o some extent in the nature of the gangue material. Since t h e a-ray can penetrate material of the density of silica very slightly-only about 0.03 mm., or 0.001 in.--it is evident t h a t t h e effective rays come only from near the surface, ayd any variation of the position of t h e active material in different samples with respect t o t h e surface would have a great influence on t h e a - r a y activity observed. It is also evident t h a t fine grin ding would not obviate t h e difficulty materially, as i t would be impossible t o produce comminution below 0.001inch. McCoy’s method of correcting for t h e absorption could be applied, but is hardly within t h e powers of the ordinary operator, does not obviate the difficulties due t o I and 2 , and involves time and labor t o a prohibitive degree for ordinary practical purposes. I n short, any efforts t o make the a - r a y method really accurate involve more labor t h a n a direct radium determination by the emanation method. There is one favorable factor, however, t o t h e advantage of t h e a-ray comparison, even for carnotite, namely, t h a t specimens from the same mine or claim 1 2
J. A m . Chem. SOC.,36 (1914), 2066. LOC.c i t
471
do not usually show such wide deviation in t h e ratio activity as those reported in Table I. per cent U308 With reference t o carnotite in general, t h e conclusion must be drawn t h a t t h e a-ray method can by no means take t h e place of a direct radium determination, nor of a uranium analysis, for purposes of sale or for scientific or commercial control. Qualitative and very roughly quantitative results only can be expected. It is not desired t h a t t h e foregoing shall discourage t h e use of t h e a - r a y method. I t s application is so simple and its results so quickly derived t h a t i t will continue t o be of great service in obtaining preliminary estimates of t h e content of radioactive materials as well as invaluable in their detection. It is merely meant t o emphasize t h a t i t cannot be relied on for final quantitative measurements. PITCHBLENDE-with reference t o pitchblende, t h e case is decidedly more favorable for t h e use of t h e a-ray method. Since t h e emanation loss is small and varies only slightly in pitchblende, t h e first difficulty is practically eliminated. The radium-uranium ratio also appears t o be constant for all different samples of pitchblende,l which eliminates t h e second difficulty. From t h e results reported in Table 11, the third difficulty also appears t o be slight, perhaps due t o t h e primary nature of pitchblende as compared with carnotite, a secondary mineral. At any rate, pitchblendes of different grades can be compared with a fair degree of accuracy. TABLE 11-SHOWINGTHE RELATIVE CONSTANCY OF THE RATIO
p E ~ ~ ~ T N T r wy ~ PITCH ~ * BLEND^^ Per cent UaOa SAMPLE (By Analysis) 1. . . . . . . . . . . . . 4.15 2 . . . . . . . . . . . . . 8.02 3. 10.55 4 . . . . . . . . . . . . . 16.4 5 . . . . . . . . . . . . . 17.3 6 . . . . . . . . . . . . . 24.7 7 . . . . . . . . . . . . . 25.3
............
a-Activity (Arbitrary Units) 0.150 0.296 0.388 0.576 0.572 0.931 0.973
Per cent UsOs a-Activity 27.7 27.0 29.2 28.5 30.2 26.6 26.0
While it would hardly be advisable t o use t h e method where great accuracy is desired, for many purposes it can be employed with convenience and satisfaction. SumATEs-one of t h e intermediate products in t h e production of radium by most of t h e different processes consists in a precipitated (Ra)BaS04. The writer has found b y experience t h a t if t h e radium content is not too high t o preclude t h e possibility of using the a-ray method, t h e results approximate fairly closely t o t h e radium content, as may be seen from Table 111. TABLEIII-sHOWING
THE APPROXIMATEc ~ N ~ T ~ N op C Y I N CRUDE
Mg. Ra per Kilo
SAMPLE
(Emanation Method)
. . . . . . . . . . . . 1.41 . . . . . . . . . . . . . .2.15 40... . . . . . . . . . . 1.32 70.. . . . . . . . . . . . 2.18 PI.. P3
(Ra)BaSOr a-Activity (Arbitrary Units) 0:71 1.20 0.73 1.28
ACTIVITY
Radium a-Activity 1.98
1.79 1.80 1.70
While t h e results for t h e sulfates are not so good as with pitchblende, they show t h a t for a quick measurement preliminary t o t h e employment of the emanation method t h e a-ray method may be used with benefit. The a-ray method has also been used very 1
Heimann and Marckwald, Jahvb. Radioakl. Elektronik., 10 (1913), 299.
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
472
successfully in the determination of other radioactive substances in small quantity for scientific purposes; but since it is the object of the present paper t o deal only with the practical methods of measuring radium itself, they do not require consideration here. THE GAMMA-RAY METHOD OB MEASURING RADIUM
Radium itself emits a-rays only, but both R a B and R a C emit y-rays which present the most convenient means of measuring radium in quantities above 0.1mg. and of not less t h a n 0.0j per cent purity. Since RaB and R a C are products resulting from the decay of radium emanation, a gas, it is necessary t o confine radium preparations in a closed vessel t o prevent the escape of gas before the measurement is made. The measurement may be carried out after the vessel has been closed for a month or more, in which case the y-radiation will have reached a constant maximum and no time correction will be necessary; the y-radiation then having become directly proportional to the quantity of radium present, as is the case of all standard tubes of radium salt which have been sealed for more t h a n a month. If the measurement is made prior t o this period, a correction must be made for the unelapsed time. This correction is readily made by reference t o the Kolowrat table, just as described in Part 111 for the emanation method.
Fro.3
I n order that the accumulation of emanation shall have taken place over a definite period of time, the starting point must be rendered exact by sealing the radium salt in a glass tube as soon after crystallization as possible. I t is first necessary, however, t o dry the salt thoroughly by raising the temperature for 20 min. or more t o 2 5 0 ' C. or higher. Otherwise, decomposition by the a-rays of any water remaining, even in the form of water of crystallization, would generate a dangerous gas pressure in the limited volume of the tube. If t h e zero period is indefinite or not known, a series of measurements must be made a t different intervals, from which the final maximum value can be calculated by comparisons with the Kolowrat table. The measurement itself consists simply of a comparison of the rates of discharge produced b y a tube with known radium content and t h a t of the unknown, each being placed successively in the same fixed position a t a suitable distance from the discharge chamber. Almost any type of electroscope may be used b y placing a lead screen, one-eighth t o one1
LOC.c i t .
1701.
12,
No. s
fourth inch thick, between the instrument and t h e tube containing the radium. A type of y-ray electroscope is shown in Fig. 3. An accuracy of about I per cent can be readily attained with ordinary precautions by the use of t h e simple aluminum or gold-leaf electroscope. Radium salts are bought and sold in the United States almost entirely on the certificate of the Bureau of Standards. The measurements are made electroscopically by the y-ray method, using standards that. have been compared with the International standard in Paris. Every radium laboratory should have a t least one secondary standard t h a t has been certified: by the Bureau of Standards. Radium emanation, which is now quite largely used therapeutically instead of radium itself, may be measured by the y-ray method exactly as radium, and is expressed in equivalent units, one curie being the amount of emanation in equilibrium with onegram of radium element. It is necessary only te allow the emanation t o remain in a closed vessel f o r 4 hrs. t o arrive a t maximum y-radiation before making the measurement. I n making this measurement, one additional correction is necessary. On account of t h e short life of radium emanation (3.8j days half period) R a C lags behind in decaying by 0.8 per cent; and since i t is RaC, not emanation, which furnishes the principal ?-rays, this correction must be deducted from t h e y-ray indication t o give t h e true quantity of emanation. If one wishes t o know simply the y-radiation and not the actual quantity of radium emanation, this correction is not necessary. The writer is indebted to the Denver Fire Clay Company for Figs. z and 3 , and t o the Sachs-Lawlor Company of Denver for permission t o describe Mr. Elzi's arrangement shown in Fig. I . The electroscopes described are made b y the Sachs-Lawlor Company and distributed b y the Denver Fire Clay Company. THE DISTRIBUTION OF CERTAIN CHEMICAL CONSTANTS OF WOOD OVER ITS PROXIMATE CONSTITUENTS By W. H:Dore DIVISION O F AGRICULTURAL CHEMISTRY, UNIVERSITY O F CALIflORNIA AGRICULTURAL EXPERIMENT STATION, BBRKBLEY,CAL.
INTRODUCTORY
I n a previous paper,' the author has proposed a scheme for separating wood into a number of proximate groups. I n addition to the groups designated, certain organic radicals (such as CH3.0 and CH2.CO) a r e known to occur in woods. Any given species is characterized by definite contents of these radicals which have accordingly become quite generally recognized as constants for t h a t particular wood. They found no place in the proposed scheme for the reason that. the quantitative relations between these so-called constants and the proximate groups were not known and i t appeared likely t h a t their inclusion would produce an overlapping of constituents. The purpose of 1
THZSJOURNAL, 11 (19191, 556.
'
