June, 1921
T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
553
The Determination of Small Amounts of Lead in Brass1 By Francis W. Glaze CHEMICAL RESEARCRLABORATORY, SCOVILL MANUPACTWRING Co., W A T ~ R B U RCONNECTICUT Y,
I n the course of research investigations in this laboratory, a n accurate, as well as fairly rapid, method was needed for the determination of small amounts of lead in brass. I n looking over the literature on the electroanalysis of lead as lead dioxide, we could find no reference t o the determination of such small amounts as those with which we had t o deal. It was therefore decided t o make a complete study of all the variables, with the idea of eventually developing a method t o fit our needs.
Cc. "Os (Sp. Gr. 1.42) per 100 Cc. 1
2 3
4
0.0055
5 6
0.0054 0.0054
7
0.0056 0.0055 0.0058 0.0056
8
9 10 Gram PbOz Calculated
PbOz Found-
-Gram
0.00341 0.0054 0.0054
0.0057
0.0030 0.0030 0.0030 0.0029 0.0028 0.0028 0.0028 0.0028 0.0027 0.0029 0.0029
0.0011 0.0010 0.0011 0.0009 0.0010 0.0010 0.0008 0.0009 0.0008 0.0005 0.0011
0.0007 0.0005 0.0004 0.0004 0.0004
1 - F ; ~ ~ ~
1
.... .... ....
0.0006
The heavy line marks the lower limit of nitric acid concentration per 100 cc., while the dotted line marks the upper limit.
EXPERIMENTAL WORK
A current of N.D.100 of 1.5 amperes and 2.9 t o 3.1 volts was used in all of this work, as the literature gave this density as the one best suited for the deposition of lead as t h e dioxide. The regular cylindrical gauze electrodes, with the anode fitting inside of the cathode, were used. Ten samples were taken, each containing a n amount of lead equivalent t o 0.0057 g. of lead dioxide. To each of these samples were added 1, 2, 3, etc., cc. of nitric acid, of specific gravity 1.42. The electrolyte was diluted t o 100 cc., and electrolyzed, the current being interrupted for 5 sec. a t the end of 0.5 hr. It was found t h a t all the lead was deposited a t the end of 1 hr., which was later found t o be practically the minimum time for the deposition of t h a t amount of lead dioxide. The electrolyte was then removed, the anode being dropped into distilled water, rinsed in alcohol, and dried a t 200' t o 230' C. for 0.5 hr. The time required from t h e moment the first of the deposit appeared above the surface of the electrolyte until the last of i t disappeared below the surface of the wash water was 2 sec. The anode with the deposit was cooled in a desiccator, and weighed. It was then cleaned, dried, cooled in a desiccator, and weighed again, the difference being taken as lead dioxide. This was found necessary, as the anode often lost as much as 0.3 mg. during a determination. This same procedure was repeated with one-half, one-fifth, and one-tenth the above amount of lead in the electrolyte. The results of these runs are contained in the table given below. For 0.001 g. of lead, 9 cc. of nitric acid per 100 cc. of electrolyte is the upper limit, while, for 0.0005 g. of lead, the acid should not be over 5 cc. Also, when the amount of lead present is 0.005 g., a t least 2 cc. of nitric acid must be present. Consequently, for our work, where the deposits range from 0.001 t o 0.0025 g., 5 cc. of acid per 100 cc. was taken as the best concentration t o use. With this acid concentration, 0.005 g. of lead can be deposited in about 1 hr. The rate of deposition can be increased by using a higher current density, but, when the density is raised t o about 4.5 amperes, decomposition of the nitric acid begins, tending t o make the electrolyte reducing. Also, when copper is present, a higher current density deposits more copper, thereby increasing the acid concentration. 1 Received
February 8,1921.
Although i t is found necessary t o interrupt the current t o obtain all the lead as dioxide when pure lead solutions are analyzed, i t is not necessary when copper is present, as lead is far enough above copper in the electromotive series of metals so t h a t any lead deposited on the cathode would immediately redissolve. Hence, all t h a t is necessary t o obtain an accurate determination of lead without interrupting the current is t o have plenty of copper in the electrolyte a t all times during the electrolysis. Large amounts of copper have no other effect a t the current density used, for the amount of copper deposited is equivalent t o 1 cc. or less of nitric acid (1.42). For the most accurate work, the electrolyte must be siphoned off, as the deposit often loses 0.2 t o 0.3 mg. when taken down by the routine method mentioned above. METHOD
An 8.643-g. sample of brass is weighed into a 150-cc. electrolytic beaker, and is carefully treated with 30 cc. of 1:1 nitric acid, after which the sample can be brought into solution with a reasonable amount of care b y means of 10 t o 15 cc. of nitric acid (1.42). It is warmed t o complete solution on a hot plate, and evaporated until cupric nitrate begins t o crystallize out, t o remove all the acid. After cooling, 5 cc. of nitric acid and a small amount of water are added. It is then warmed until all the crystallized salt dissolves, diluted t o volume, and electrolyzed a t a current of N.D.100 of 1.5 amperes and 2.9 t o 3.1 volts. At the end of 1 hr., all the lead will have been deposited. However, it is best t o add a little distilled water and continue the current for about 10 min. longer, watching t o see if any lead is deposited on the clean surface. The electrolyte is siphoned off, the anode being washed with distilled water and alcohol, and finally dried a t 200' t o 230' C. for 0.5 hr. It is then cooled in a desiccator, and weighed. After cleaning and drying, i t is weighed again, the difference being lead dioxide. The weight of the lead dioxide in grams, multiplied by 10, gives the percentage of lead in the brass. This method will work for all amounts of lead less than 0.06 per cent. No doubt, i t will work for larger amounts, but no study has been given t o t h a t phase of the problem. It has proved very satisfactory and has given most concordant results.
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
554
SUMMARY
The electrolytic method for the determination of lead as lead dioxide has been investigated with the idea of using it t o determine small amounts of lead in brass. The methods given by Dr. E. F. Smith in his
Vol. 13, No. 6
book “Electro-analysis,” and by Price and Meade in their book “Technical Analysis of Brass,” under spelter analysis, with a few modifications, are found t o apply very well. The current density and the acid concentration are the most important variables.
LABORATORY AND PLANT The Manufacture of Citric Acid from Lemons‘ By C. P.Wilson
I
RESEARCH LABORATORY, CALIFORNIA FRUITGROWERS EXCHANGE, CORONA,CALIFORNIA
The first serious attempt t o convert the lower grades of California lemons into by-products was made in 1898 a t National City, San Diego County. Other factories for the production of various products from citrus fruits have been started a t various times a t Pasadena, Redlands, Santa Ana, Riverside, and other places. An excellent account of these has been given by Will.2 Work along similar lines in connection with Florida oranges has been published by McDermotta and by Walker The United States Department of Agriculture became interested in the possibility of developing a citrus by-products industry in this country, and in 1907 sent Mr. E. M. Chace t o Italy t o study similar industries there.6 Mr. Chace made a survey of the lemon industry in California in 1908, and as a result of his work the Department established the Citrus By-products Laboratory in 1911 a t Los Angeles. The early work of this laboratory was done by Mr. H. S. Bailey and the author under the direction of Mr. Chace, who has been in charge of the laboratory since its beginning. The Citrus By-products Laboratory secured accurate data on the methods applicable t o the manufacture of citric acid, and the yield t o be expected from lemons. It must be remembered t h a t the average haul by which citrus fruit raised in California reaches its market is about 2500 miles. This precludes the shipment of anything but sound fruit of good appearance and keeping quality. There is necessarily left a large quantity of fruit t h a t is not fit t o pack and ship. This is culled out for reasons such as: irregular shape, oversize, undersize, frost damage, heat damage, clipper cuts caused by careless picking, thorn pricks, wind scars, thrip marks, excessive scale, or any sort of mechanical injury or indication of decay or infection of any kind. The steps in the process of manufacture of citric acid may be readily followed by means of the accompanying sketch. I
E X T R A C T I O N OF JUICE
All the citric acid in a lemon is contained in the 1 Read before the Southern California Section of the American Chemical Society, Los Angeles. c a l . , December 1920. 2 THIS JOURNAL, 8 ( l e l e ) , 78. Ibid., (I (Isle), 136. 4 Florida Agriculturai Experiment Station, Bulletin 186. IBureau of Plant Industry, U. S. Department of Agriculture, B u l k l h J
180.
juice, so t h a t the separation of juice from the pulp may be considered the first step in the recovery of the acid. The fruit is shoveled or dumped on t o a broad belt conveyer and, if other products than acid are t o be made, is graded t o give the kind of fruit needed for such a product. Any lemon can be used t o make citric acid, though, of course, the yield varies enormously from as low as 15 lbs. per ton from badly frozen lemons t o 50 lbs. or more from the thin-skinned juicy lemonettes. It is interesting t o note t h a t the effect of frost is t o decrease the amount of juice in t h e fruit and also the percentage of acid in the juice which remains. The fruit passes from the grading belt by way of a bucket elevator t o a pair of cutting knives which tear the lemons coarsely and drop them into a set of wood roller crushers which thoroughly bruise the fruit and press out some juice. The crushed fruit drops into the hopper of a continuous screw press where most of the juice is removed. The continuous presses are similar t o those used for pressing moisture, fat, or oils from garbage, fish scraps, copra, vegetable seeds, etc. From the first press the juice runs t o the measuring tank, while the pulp is passed through a soaking box where it is saturated with water. From this box t h e wet pulp is dumped into another continuous press and the juice goes t o the same measuring tank as did the first juice. Pulp from the second press is elevated t o the hopper of a third press, receiving a spray of water as i t ascends the elevator. Juice from the third press serves as maceration water for the first soaking, while the pulp passes out and is used as fertilizer. One ton of lemons contains on the average about 70 lbs. of total acid (calculated as crystallized citric acid). Using the extraction process described above, 85 per cent or more of this acid is obtained in the juice. Pure pressed lemon juice contains from 6 t o 7 per cent citric acid, but on account of the dilution by maceration water the mixed juice obtained in factory practice averages about 4 per cent acid and contains about 5 t o 5.5 per cent of total solids. The juice contains about 0.5 per cent of insoluble solids and is rather thick and pulpy. It is stored in wooden tanks of about 57,000 liters capacity, in which it is allowed t o undergo fermentation for about 4 or 5 days in warm
