dS.4 LY TICS L EDI T I O S
3 9s Method
A titration is performed by connecting the electrodes to the terminals, X , of either device, and setting the pointer of the milliammeter in the middle portion of the scale by varying the resistance RBof Figure 1, or R4 of Figure 2 . The solution should be stirred at a constant rate and the titrating reagent allowed to run quite rapidly into the solution from the buret until the needle begins to move. K h e n the approach of the equivalence point is indicated by the irregular movement of the needle, the rate of discharge from the buret is reduced to 10 or 15 drops per minute. After one or two titrations have been performed in which the magnitudes of the excursions have been recorded, it is possible to stop the titration when the largest deviation is observed, which is the inflection or equivalence point. Experimental Results
Successive portions of a 0.05 +If lead nitrate solution were withdrawn by means of calibrated 50-cc. pipet and titrated
5’01. 2 , s o . 4
with 0.1 Ar potassium chromate. The following table shorn the results of a series of such titrations. TITRhTED
KzCrOa USED
THEORI$TICAL
cc
cc.
cc.
cc.
50 00
19.97 19.95 19 98 19.95 19.98 19.97 19.07
19.955
+0.015 -0.005 +0.025 -0.005 -co.025 t0.015
Pb(NOa)?
KzCrO4
DEVIATIOV
i-0.015
Further work is being done upon the electrometric determination of lead. Literature Cited (1) Calhane a n d Cushing, IND.ESG. C H m f . , 16, 1118 (1923). ( 2 ) Ewing, J : A m . Chem. Soc., 47, 301 (1925). (3) Goode, I b i d . , 44, 26 (1922); 47, 2483 (1925); J . O p l i c a l Soc. Am.,17, 59 (1929). (4) Treadwell, H e h . Chim. Acta, 8, 89 (1925).
Effect of Degree of Pulverization and Weight of Samples on Quantitative Analyses’ With Particular Reference to Plant Tissues R. C. blalhotra HULLBIOLOGICAL LABORATORY. USIVERSITY
I-INFLUENCE OF PARTICLE SIZE OF SAMPLE
The effect of particle size and weight of sample on the quantitative determination of various chemical constituents of plant tissues has been studied. The data indicate that, for practical purposes, material passed through 60-mesh sieve is satisfactory to use. The data also point out that, for the tissues studied, from 3 to 4 grams of material are most desirable. Less than this amount and larger than 6 grams do not Seem to be satisfactory. Some possible explanations of such results have been given.
bIOST chemical ]ab+ ratories dealing JTith plants it Seems to be ac cepted practice to pulverize the sample so fine that it can pass 100- to 130-mesh sieve (12). Such fine p o w d e r s have been considered necess a r y for the quantitative estimation of organic and inorganic constituents of plant tissues. To secure such a fine sample only takes not a great deal of time, but also some contamination is liable to take place. This is particularly true of hardwoods. Extensive experiments have therefore been conducted to see if this extra n-ork is worth the effort.
I
Review of the Literature
Many chemists have emphasized the importance of finely powdered substances in chemical analysis. Blanchard and Phelan ( 1 ) state: “In chemical reactions in which solid substances are involved, the reaction is limited to the surface of the solid, and for this reason i t is evident that it must be much slower than reactions which take place between dissolved substances; it is also evident that the more finely powdered a solid substance, the greater is its surface, and therefore more rapidly it will react.” This refers t o inorganic substances. Experiments of Ostwald (17), confirmed by Hulett (Io), have shown that the solubility of a solid depends not only upon the temperature but also on the dimensions of the solid particles which are in contact with the solution, and is greatest €or extremely fine particles. J7aret (23),working with red and yellow oxides of mercury, 1
Received August 19, 1930
OF CHIC.4G0, C H I C A G O , I L L
has attempted to show that the transformation frorn one variety to another produces 110 thermal effect but from a physical poilit of view they differ only in the size of the particles. This has also been discussed by Chesneau ( 3 ) . Scott (19) also mentions the fact that, inasmuch as the usual object of pulverization is to increase the surface upon which chemical action is to take place, the particles should be fine. Treadwell (22) also says that solid substances dissolve more quickly when reduced to a fine powder. Moreover, when a material undergoes a chemical change an insoluble substance is often formed, which during the process of solution may form a protective coating over the particles of the material that have not been acted upon. This danger is diminished if the material is finely powdered. This practice of grinding samples into very fine powders has certain disadvantages, however. If the material is hard, as in the case of metals and hardwoods, there is always some contamination from the material of which the grinding apparatus is constructed, as found by Hempel (8). He states that a n agate mortar and pestle lost 0.052 gram in pulverizing 10 grams of glass. Blasdale ( 2 ) also mentions the effect of pulverization in the contamination of the sample. The sample may undergo slight decomposition during the grinding operation. Such changes take place in plant tissues, even in the hardwood samples of pear and apple, as brought out by Lincoln and blulay (11). A number of investigators have pointed out the effect of grinding on the moisture content of a sample. If the sample is practically dry, it is likely to absorb considerable moisture \$lien dried in the air, as pointed out by Hillebrand (9). On
ISDC-STRIAL d S D EYGINEERISG CHEMISTRY
October 15, 1930
the other hand, grinding often causes loss of moisture, particularly in the case of substances containing water of crystallization or superficial moisture. This difficulty is recognized by Lunge ( I S ) who says, “Since change in the amount of moisture is almost unavoidable during the final grinding, the final sample is either dried in a drying oven and then weighed out in the dry condition for analysis or the moisture is determined separately in another sample and the results calculated on the dried substance.” The heat produced by grinding may not only serve to expel moisture from the sample, but i t may also cause chemical changes (15). It is thus seen that fine grinding may account for many cases of divergent results in the hands of different chemists analyzing the same material. Experimental
The experimental work was done on uniform three-year-old McIntosh apple and Bosic pear twigs, on tomato plants grown from seeds which mere obtained from a single plant and also on spinach from uniform seeds. Tomato and spinach were grown for six months under the same conditions. The plant tissues were cut into small pieces with shears and their moisture content was determined to four decimal places (constant weight). After drying, each kind of tissue was divided into I1 lots. Each lot was first ground in a grinding machine manufactured by the Enterprise Manufacturing Company and then pulverized in W l e y mill in such a manner that lots could pass through sieves of various sizes. From 3 to 3.5 grams of the material were used out of each lot. Duplicate determinations were made of each chemical constituent and analyses were repeated till the duplicates checked to the second decimal place. Total proteins, sugars, starch, hemicellulose, pentosans, and ash were determined. Total nitrogen was estimated by the Arnold-Gunning modification of the Kjeldahl method, following the directions laid down by AIathews ( I C ) . Sugars were analyzed by the iodometric method as described b y Shaffer and Hartniann (20). Starch was digested b y standardized solution of saliva as recommended by Gardner (e),and the resulting sugars mere estimated by the same method as used for the sugars. Hemicelluloses were determined by hydrolyzing the sample left after digesting starch with 2.5 per cent hydrochloric acid for 4 hours in a pan of water kept under an electric hot plate. Cleinents (4)has shown this to be the only way to obtain comparable results for hemicelluloses. Pentosans were deterTable I-Effect
399
mined by the modified method of hlalhotra ( I j ) . Ash was determined by burning the samples to constant weight in a n electric muffle. Presentation of Data and Discussion
The data in Table I indicate the results of the analyses. I t will be seen that percentages are lower for samples which passed through the 30-, 40-, and 50-mesh sieves. I n genera1 the results are less uniform and lower for powders which passed through the 30- and 40-mesh than for 50-mesh sieve. With the 60-mesh sieve the results are more uniform and higher than those in the first three columns. The figures for the remaining columns are in general about the same as those given for the 60-mesh sieve. The figures for total proteins and ash are practically the same for all meshes; any slight differences may be attributed to experimental error. Since in determination of both these constituents complete digestion and burning are desired, differences in particle sizes within the limits studied did not make any variation in the results, whereas in the other determinations such as for sugar, starch, hemicelluloses, and pentosans, in which the powder had less drastic treatment the size of particles was of more importance. Hemicelluloses gave variations as great as 35 per cent. This may be explained by the fact that, since hemicelluloses are coniparatively inert material of cell walls, if the size of the particles is large seyeral walls offer more resistance to the acid than n-here there are fewer walls as in the case of fine powders. Hon-ever, beyond 60 meshes, this has little effect. From the data presented in Table I it may be concluded that for the quantitative determination of various carbohydrates, total proteins, and ash in such plants as the apple, pear, spinach, and tomato, a powder fine enough to pass through a 60-mesh sieve is satisfactory. Larger particles give low and non-uniform figures while finer particles on the whole do not give any better results. The extra time, labor, and precaution in securing finer powders does not therefore seem to be necessary. Powders passed through 30-, 40-, and 50-mesh sieves are unsatisfactory except for the determination of proteins and ash. 11-EFFECT
OF W E I G H T OF SAMPLE
Experiments n-ere also conducted to see if differences in the vieight of the sample would make any difference in chemical analysis, and, if there is any difference, to determine the weight of the sample n-hich will giye the maximum uniform results.
of Fineness of Material on Chemical Analysisa (Results calculated on dry weight basis)
TISSUE.4NO CHEMICAL COSSTITUESTS
: P ,c
CI ,o
7o-hIESH
SO-MESH QO-~IESH
70
rI’ 6
n ,O
00
C’ IC
7%
n io
15.7 3.4 3 3 26 0
15.6
I!,,”
15.7 3.5 3.4 27.2 11.7 2.1
15.6
3.6 3.3 27.9 11.7 2.1
15.9 3. 5 3.2 27.3 11.6 2.1 17.2 +.3
17.1 4.1
M C I S I O S H APPLE:
15.7 3 0 2.8 25.7 9.2 2.1
15.6 3.4 3.1 27.0 11.6 2.1
15.6 3.3 3.4 27.0 11.8 2.2
15 8 3 6 3 3 27.2 11.8 2.3
16.9 3.4 2.5 22.7 10 1 2 2
17.1 4.1 3.0 24.0 14.6 2.3
17.1 4.2 3.1 24.6 14 6 2.3
17.2 4.2 3.2 24.2 14.6 2 3
17.1 4.3 3.2 24.8 14.8 2.4
17.1 4.2 3.1 24.0 14.8 2.3
4.8 11.2
4.8 11.9
4.9 13.2 4.5 9.9 4.0 2.3
4 9 13.6 4.3 9.0 3 9 2.4
3 .0 14.0 4.6 10 0 3.9 2.5
5 0 14.0 4.3 10.4
4.5 S.6 4.4 S.6 5.3 2.4
4.8 8.6 4.4
4.8 8.9 4.3 8.7 5.5 2.5
4.7 8.9 4.7 8.6 5.4 2.3
Proteins Total sugar Starch Hemicelluloses Pentosans Ash BOSIC PEAR:
Proteins T o t a l sugar Starch Hemicelluloses Pentosans Ash SPINACH:
Proteins Total sugar Starch Hemicelluloses Pentosans Ash
3 0
3.4
7.6 2.5 2.1
8 3 3 1 2 1
4.9 13.2 4.3 10.1 4.0 2.4
4.6 4.6 Proteins 6.1 6.3 Total sugar Starch 2.6 3.1 Hemicelluloses 6.9 5.8 3.8 4.1 Pentosans Ash 2.4 2.4 4 a l l carbohy.drates wcre figured a s dextrose
4.6 7.1 3.5 7.7 4.5 2.4
4 5 8.5 4.3 8.7 5.3 2 5
.
4.8 10 6 2.7 6.9
2.1 2.0
;:
TOMATO:
s.I .. J9
2.4
-3.2
24.3 14.5 2 4
4.8 13.9 4.9 10. 7
4.1 2.1
:.; 4.6 S 6 6 4 2.3
3.5 3.2 27.2 11.6 2.3
17.1
;:;
3.6 24.0 14.9 2.3
24.9
4.9 13.6 4.9 10.7 4.6 2.3
4.9 13.4 4.4 10.4 4.1 2.2
4.7 8.7 4.5 8.I 5,3 2.4
4.8 8.7 4.6 8.8 5.4 2.5
14.7
2.3
Vol. 2, No. 4
4 X A LYTICA L EDITI0.V
400
of W e i g h t of S a m p l e on C h e m i c a l Analysis" (Calculated on d r v weight basis) 2 5 3 0 4 0 1.5 2.0 GRAMS GnAm GRAMS GRAMS GRAMS
Table 11-Effect
-
TISSUE A N D CHEMICAL COKSTITUENTS
I
5 0 GRAMS
6.0 GRAMS
7.0 GRAMS
8.0 GRAMS
0.5 GRAM
1.0 GnAM
70
70
%
70
%
70
%
70
%
%
70
14.3 2.1 2.1 24.9 10.0 2.0
14.7 2.7 2.5 26.0 10.3 2.0
14.9 2.7 2.5 26.1 10.9 2.1
151 2.9 2.7 26.6 10.9 2.1
15.2 3.1 3.0 26.4 11.1 2.1
15.7 3.5 3.0 26.9 11.9 2.2
l5,Q 3.4 3.1 27.0 11 9 2.2
15.9 3.5 3.0 27.1 11.9 2.2
16.0 3.1 2.9 26.1 11.6 2.2
15.6 3.8 2.9 25 9 11.3 2.2
15.1 3.2 2.3 26.6 11.5 2.2
15.8 3.3 2.3 22.0 13.7 2.0
16.2 3.7 2.3 22.4 14.0 2.0
16.5 4.0 2.5 23.0 14.0 2.1
16.8 4.0 2.9 23.3 14.2 2.1
17.0 4.3 3.1 24.1 14.5 2.4
16.6 4 1 3 2 24 0 14 2 2 4
16.5 14 0 3 1 24.0 14 0 2 4
3.8 12.0 3.3 8.2 1.0 1.8
4.0 12.1 4.0 8.6 1.5 2.0
4.3 13.0 4.1 9 0 2.6 2.0
4.7 13.0 4.1 9.0 3.4 2.0
4.9 13.3 4 3 10 4 3.9 2.3
4 13 4 10 4 2
4 12 4 10 3 2
4 0 Proteins 3.7 8 1 Total sugar 7.2 3.4 3.8 Starch 8 0 Hemicelluloses 8.0 Pentosans 4.9 5 0 2.0 Ash 2.0 a All oarbohydrates were figured as dextrose.
4.1 8.1 4 0 8 2 5 0 2 3
4.3 6.3 4.0 8 2 5.3 2.3
MCINTOSH APPLE:
Proteins Total sugar Starch Hemicelluloses Pentosans Ash BOSIC PEAR:
Proteins Total sugar Starch Hemicelluloses , Pentosans Ash SPINACH: Proteins Total sugar Starch Hemicelluloses Pentosans Ash TOMATO:
Review of Literature
Rose (18) states t h a t the most convenient weight to use is 2 or 3 grams when there is plenty of the substance. Griffin (?), speaking of the analysis of wood, paper, etc., recommends 5-gram samples. Foulk ( 5 ) invites attention to two considerations: (1) A small sample (0.5 gram or less) is easily dissolved. On the other hand, all errors of weighing the inevitable slight gains and losses in the course of the analysis make a large percentage of errors. (2) Larger samules are more difficult to dissolve. The advantages age that, -owing to the large amount of material used, the errors of weighing and loss or gain in various chemical operations are relatively slight. He recommends larger samples.
From a large number of workers dealing with the analysis of plant products, i t may be concluded that no definite weight of sample is chosen. The writer found very little experimental evidence t o indicate the influence of the weight of the sample on the chemical analysis of plant materials. The same is more or less true of inorganic material ( 2 1 ) . However, the character of the material, size of the various particles, and uniformity of composition are factors governing the determination of the amount to be taken as the sample unit, and a n answer to this unsettled question seemed desirable. Experimental
The tissues used were the same as for Part I and mere treated the same way, except that all samples were passed through a 60-mesh sieve. The samples were weighed out in triplicate, sometimes in fives, ranging from 0.5 to 8.0 grams. I n every case check within t1v-o decimal places was tried, although in the very low weights this was found to be impracticable. Analyses were made for only those constituents which were determined in Part I, and the same methods were used. Presentation of Data and Discussion
The results are presented in Table 11. The 0.5-gram samples gave the lowest figures. The figures increased gradually with the increasing weights u p to 3.0 and 4.0 grams beyond which they fluctuated although increased on the whole up to 5.0 and 6.0 grams. With the 7.0- and 8.0-gram samples generally the results were lower, and in most cases for the 8.0-gram samples they were lower than for 3.0 and 4.0 grams.
4.9 13.2 4 3 10 1 3 6 2.3
4.9 13 3 4.3 10.1 3.9 2.5
4.9 13 2 4 3 10 1 4.2 2.5
4.9 13 5 4.4 10 2 3.9 2.4
4.6 8.6 4.3 8.5 5 5 2.6
7 0 2 1 3 1
4 4 8 3 4 1 8 5 5.3 2.5
5 9 0 0 8 3
4.2 8.0 3.9 8.1 5.0 2.5
This seemed to be more or less true for all the plant tissues studied. It would thus seem that samples weighing 2.5 grams or less are unsatisfactory, because they yield lower percentages of the yarious chemical constituents than are actually representative of the samples. Samples from 3.0 and 4.0 grams are sat'isfactory. Samples larger than 5.0 grams are not desirable, and those weighing 7.0 and particularly 8.0 grams are unsatisfactory because they yield loner results although not as low as 0.5 to 1.5 grams. There may be several reasons why smaller and larger samples are unsatisfactory to use. I n the smaller samples there is more chance of error in weighing during the course of analysis, possibly due t o the destruction of the constituents to be determined by a larger unit volume of reagents per unit weight of the material. On the other hand, with the largest samples lower yields may be due to too little reagent to react with the material for the various determinations. Since in most biochemical analyses where weight is chosen a t will, no particular attention is paid t o the volume of the reagent to be used (it is a common practice to use the volume indicated in various laboratory outlines), the unit weight of material to be analyzed is greater than the unit volume of the reagent for the complete reaction. Acknowledgment
I t is a pleasure to acknowledge the many helpful discussions with D. R. Hoagland, Department of Agricultural Chemistry and Plant Physiology, a t the University of California, in connection with t'his work; and also the cooperation of H. R. Tukey, chief hort,iculturist of the S e w York Agricultural Experiment Station, Geneva, Y. Y., in supplying some twigs used in this study. Literature Cited (1) Blanchard and Phelan, "Synthetic Inorganic Chemistry," p. 10, XViley. 1922. (2) Blasdale, "Quantitative Analysis," p. 28, Van Xostrand, 1924. (3) Chesneau, "Theoretical Principles of Methods of Analytical Chemistry," English translation by Lincoln, hlacmillan, 1910. (4) Clements, P h . D . Thesis submitted t o University of ChicaLo, 1929. ( 5 ) Foulk. "Quantitative Analysis," p. 32, XcGraw-Hill, 1914. (6) Gardner, Plant Phvsiol., 4, 405 (1929). (7) Gri!En, "Technical Methods of Analysis," p. 289, McGraw-Hill, 19'21. (6) Hempel, Z. a n g e w Chem., 14, 843 (1901). (9) Hillebrand, J. A m . Chem. Soc., 30, 1120 (1908). (10) Hulett, Z . p h y s i k . Chem., 37, 385 (1901).
.
I X D USTRIAL A1VD EXGINEERIXG CHEMISTRY
October 15, 1930
(11) Lincoln a n d Mulay, Plant Physiol., 4, 251 (1929). (12) Link, J . A m . Chem. Soc., 51, 2506 (1929). (13) Lunge, “Technical Methods of Chemical Analysis,” Vol. I, p. 12, Van Nostrand, 1908. (14) Malhotra, J . I n d . Chem. Soc., in press. (15) Manzelins, “Sveriges Geol. Undersokning Arsbok,” Vol. I (1907). (16) Mathews, “Physiological Chemistry,” p. 994, Wood, 1925. (17) Ostwald, Z . physik. Chem., 17, 183 (1895).
401
(18) Rose, “Practical Treatise of Chemical Analysis,” translated by Normandy, p. 583, William Tegg and Co., London, 1847. (19) Scott, “Standard Methods of Chemical Analysis,” Vol. 11, Van Nos. trand, 1925. (20) Shaffer and Hartmann, J. B i d . Chem., 46, 349 (1920). (21) Sharwood and Bernewitz, Bur. LIines, Repts. of Inue>lc&ionr 2336. (22) Treadwell-Hall, “Analytical Chemistry,” p. 51, Wiley, 1930. (23) Varet, 2. physik. Chem., 17, 622 (1896).
Rapid Method for Determining Calcium in Lead Alloys of Low Calcium Content’ Leon I. Shaw, Charles F. Whittemore, and Thor H. Westbp WESTERY
ELECTRIC COXPANY, HAWTHORSE n‘ORKS,
HE purpose of this investigation was to develop a 30-min-
T
Ute method for determining calcium in a lead-calcium alloy. The method previously used in the writers’ laboratories was an adaptation of usual standard procedures and required about 18 hours for a complete determination. Although this was satisfactory a t the time it was developed about two years ago, the need for a much more rapid method has since appeared. Saturally consideration was given to spectrographic methods but, as it was desirable to have a method available for use in laboratories having no suitable spectrographic equipment, the best solution seemed to be to shorten the 18-hour routine method if possible. By devising means of accelerating the decomposition of the sample and by eliminating the necessity for allowing the precipitated calcium oxalate to stand overnight, the procedure was brought within the requirements of time and accuracy. The 18-Hour Method
The l&hour method was based on the usual permanganate titration subsequent to the separation of calcium as calcium oxalate. I n this procedure the sample is dissolved in dilute nitric acid, the lead precipitated with sulfuric acid and filtered off. The filtrate is made ammoniacal and the calcium precipitated with ammonium oxalate. The calcium oxalate is filtered off, dissolved in sulfuric acid, and titrated with permanganate. The precision of this method was established by determining the calcium in solutions of lead nitrate t o which a known amount of calcium had been added. The results are shown in Table I. T a b l e I - D e t e r m i n a t i o n s of C a l c i u m i n T w o S y n t h e t i c L e a d - C a l c i u m Solutions by 18-Hour P e r m a n g a n a t e Method No CALCIUVSOLGHT CALCIUM FOW\D ERROR Per cent Per cent Per cent 0.000 0.039 0.039 -0.001 0.038 0.000 0.039 0.000 0.039 0.000 0.039 +0.001 0.040 Av. 0 039 0.000
Av.
0.061
0.000
Preliminary Investigation
Tests with fuming nitric acid proved that this reagent would be a suitable solvent for the rapid decomposition of the sample. 1
Received June 20, 1930.
Presented before t h e Division of Physical
and Inorganic Chemistry a t t h e 79th Meeting of the American Chemical
Society, Atlanta, Ga., April i t o 11, 1930.
CHIC.4G0,
ILL.
The reaction is rather violent, but easily controlled by adding a few cubic centimeters of cold water. Oxalic acid was first tested as the precipitant, but satisfactory precipitation of the calcium oxalate was obtained only when a large excess of ammonia was added and the salts thus formed retard the filtration. It was then found that the solubility of the precipitated calcium oxalate was suppressed by adding 95 per cent ethyl alcohol to the ammoniacal solution after removal of the lead. Taking advantage of this fact, calcium may be precipitated with ammonium oxalate and filtered off after boiling only 2 minutes and subsequently settling only 5 minutes. The calcium oxalate precipitate contains a very small amount of lead, which is not present in sufficient amount to affect appreciably the precision of the results. T a b l e 11-Comparison of R e s u l t s of D e t e r m i n a t i o n s of C a l c i u m i n a L e a d - C a l c i u m Alloy b y 1 8 - H o u r M e t h o d a n d R a p i d M e t h o d RAPID METHOD 18-HOvR METHOD Deviation Deviation NO. Calcium from mean Calcium from mean Per cent Per cent Per cent Per cent 1 0,029 0,000 0.030 +O.OOl 2 0.030 +0.001 0.030 +0.001 0.000 0.030 +0.001 3 0,029 0.000 0.031 +0.002 4 0,029 5 0.028 -0.001 0.030 +O.OOl 6 0.030 $0,001 0.028 -0.001 7 0.029 0.000 0.028 -0.001 8 0.029 0.000 0.029 0.000 9 0.030 +0.001 0.029 0.000 AV. 0.029 0 000 0 029 1 0 001
Rapid Method Procedure
Place a 20-gram sample, prepared to pass a 40-mesh screen, in a 400-cc. beaker, add 25 cc. of fuming nitric acid, and then add 95 to 100 cc. of boiling water. Place the beaker on the hot plate. As the reaction is rather violent, a few cubic centimeters of cold water may have to be added to prevent loss from foaming. T h e n the sample is completely dissolved (in 4 to 5 minutes), add 25 cc. of 1: 1 sulfuric acid, stir, and filter on a n asbestos pad. K a s h two or three times with hot water and discard the precipitate. Keutralize the filtrate with ammonia using litmus paper as an indicator. Then add 15 cc. excess ammonia and stir, Add 30 cc. of 95 per cent ethyl alcohol and mix well. Add 2 grams of ammonium oxalate and boil the solution for about 2 minutes. Remove from the hot plate and rinse the cover glass and the sides of the beaker. Allow the precipitate to settle for 5 minutes without cover glass. Filter on an asbestos pad reenforced with an S.and S. Blue Ribbon filter paper or the equivalent. TTash three times with hot water. Transfer the pad to the original beaker and rinse the Gooch crucible using as little water as possible. Add 30 cc. of 1:1 sulfuric acid followed by 250 cc of boiling water and place on the hot plate for about
