Aug., 1914
T H E JOC'R,VAL O F 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
t o use i t every time t h e article is laundered. This is because t h e oxycellulose formed t h e first time bleach is used yields t h e objectionable yellow substance already spoken of when alkalies are used subsequently, a n d t h e use of more bleach becomes necessary. These experiments with bleaching agents seem t o show t h a t if excessive damage is t o be avoided, some sacrifice in t h e color of t h e finished articles will need t o be made. This might be accomplished either by using hydrosulfites, or other reducing agents. or by using much smaller quantities t h a n are now considered necessary, of some of t h e oxidizing agents in use a t t h e present time. CONCLUSIONS
I-The bleaching a n d treatment of fabrics with acids are t h e most harmful parts of t h e process now in general use in steam laundries. The bleaching not only weakens t h e fabrics, b u t also produces oxycellulose, which yields a n objectionable yellow substance when treated with even dilute solutions of alkalies. The hydrolysis of cellulose produced by t h e hydrogen as ion in acid solutions weakens t h e fibers. Thorough rinsing is essential t o remove as much of the acid used as possible. The quantities of bleaching solution a n d acid used should be kept as small as possible. n-The use of alkalies in excess affects prejudicially t h e color a n d strength of fabrics, a n d leads t o t h e formation of much lint. 3-Contrary t o t h e common belief of launderers, s o f t water is superior t o hard water for all purposes, rinsing included. 4-The deposition in the fibers of insoluble salts or the crystallization of soluble salts does not greatly affect t h e wearing qualities of fabrics. j-The use of mineral acids in t h e laundry cannot be generally recommended, because of t h e extent t o which t h e y a t t a c k cellulose if they are not thoroughly removed by rinsing. 6-One cause for t h e yellowing of fabrics composed of cellulose on standing is t h e formation of yellow products by t h e action of hydroxyl ions on t h e oxycellulose which is formed during t h e bleaching process. 7-A saving in t h e quantity of bleaching solution required a n d a n improvement in t h e color produced are possible when t h e bleaching is done as a separate process. The usual practice is t o combine washing a n d bleaching. 8-Hydrosulfites may be used for effecting t h e bleaching, b u t t h e color obtained is not as good a s t h a t produced by hypochlorites. 9-Magnesium hypochlorite solutions present no advantages over t h e slightly alkaline solutions of sodium hypochlorite now employed, as far as their destructive actions are concerned. Io-Ozone produces a satisfactory color when allowed t o act o n fabrics before or during t h e drying which is effected in t h e drying rooms. T h e fabrics are less attacked t h a n in the present method, b u t t h e ozone process is not well received by t h e trade because it necessitates extra handling of t h e articles, a n d increases unduly t h e length of time necessary t o complete t h e laundering operation. DEPARTMENT OF INDUSTRIAL CHEMISTRY OF KANSAS, LAWRENCE UNIVERSITY
649
A PRACTICAL METHOD FOR THE PREPARATION OF DRY STARCH, SOLUBLE IN COLD WATER, FOR USE AS AN INDICATOR' By ROBERThf. CHAPIN Received April 18, 1914
When, several years ago, t h e necessity arose for preparing a large quantity of dry starch which should be readily soluble in cold water and appropriate for use as a n indicator in iodine titrations, no description of a sufficiently practical method of preparation could be found. Wroblewski2 prepared t h e desired form of starch by running a concentrated solution of soluble starch, in a t h i n stream, and with vigorous stirring, into a large excess of alcohol, followed by washing with absolute alcohol a n d ether, a n d drying in vacuo. He stated t h e resulting product t o be soluble in cold water up t o about 4 per cent, and t o yield a pure blue with iodin. His original soluble starch was prepared by digesting rice starch with I per cent caustic potash solution. I n t h e present work, Wroblewski's method of precipitation, etc., was found effective, b u t 'for the preparation of t h e original soluble starch, Lintner's3 method of digestion with acid proved more satisfactory. T h e first preparations, made in 1911, were of good quality, b u t were obtained through a series of tedious and expensive processes. Since t h a t time, through the repeated preparation of large quantities of t h e material, t h e process has become so simplified a n d standardized t h a t it is believed t o be worthy of publication. I n t o a j-liter round flask with a long neck are brought 400 grams potato starch, 2300 cc. distilled water, and lastly, 80 cc. normal hydrochloric acid. T h e flask is well shaken t o wet and distribute t h e starch thoroughly, a n d is floated in a kettle of water previously brought t o vigorous boiling. T h e neck of t h e flask rests conveniently on t h e side of t h e kettle a t a n angle of a b o u t 4 5 O , a n d as soon as t h e flask is brought into t h e b a t h i t is smoothly and continuously rotated about its longitudinal axis. As t h e flask becomes hot t h e starch forms a n evenly distributed uniform jelly, which, in about seven minutes from t h e time of starting, begins t o liquefy a n d t o fall away from t h e wall of t h e flask. When this stage is reached t h e mouth of t h e flask is loosely closed with a n inverted beaker and t h e flask l e f t in t h e boiling b a t h with a n o c c a s i v a l rotation until t h e mobile liquid shows no lumps of gelatinized starch remaining-1 t o I ' / ~hours. T h e flask is t h e n rapidly cooled in running water until i t can be comfortably handled (about 50' C.), t h e n methyl orange is added, followed b y concentrated ammonia t o alkaline reaction. Next is immediately added 800 cc. of g j per cent alcohol, a n d , after thorough mixing and standing for a few minutes t o allow air bubbles t o separate, t h e liquid is strained through moderately coarse muslin. The addition of this proportion of alcohol notably reduces t h e viscosity a n d increases t h e permanence of t h e solution. Starch will separate some time after t h e solution has become cold, b u t with proper management ample time remains for t h e subsequent operations. I n fact, 1
Printed by permission of the Secretary of Agriculture.
2
Ber., SO (1897). 2108. J . fur p r a k t . Chem., Sl (1886). 378.
3
T H E J O U R N A L O F I i Y D U S T R I A L A N D ENGI-VEERING C H E M I S T R Y
6 50
after experience h a s been gained, t h e a m o u n t of water, a n d in due ratio t h e t o t a l a m o u n t of alcohol, m a y be somewhat reduced. T h e solution, still a t 40 t o 45' C., is r u n through a n u m b e r of fine jets into four liters of g j per cent alcohol, with continuous stirring. T h e whole is left for at least 48 hours with a n occasional thorough stirring after which most of t h e s u p e r n a t a n t alcohol is decanted a n d t h e rest used t o transfer t h e starch t o a two-quart percolator provided with a filter plate which is covered with filter paper or cloth. Here i t is percolated with 9j per cent alcohol, being stirred u p with a stick at intervals t o prevent t h e formation of clumps or fissures, until alcohol comes through t h e percolator of a specific gravity indicating a strength of 90 per cent. T h e starch is t h e n transferred t o a Buchner funnel, well drained with suction a n d spread out t o d r y i n a moderately warm place. T h e resulting product is a fine white voluminous powder, more or less compacted t o friable lumps which completely disintegrate under slight pressure. I n less t h a n a minute, a little of i t €hrown i n t o cold water dissolves sufficiently t o yield a good blue upon t h e addition of potassium iodide a n d iodine. Moistened with water o r dilute alcohol, i t becomes g u m m y a n d subsequently dries o u t t o a horny mass, very slowly soluble in cold water. T h e efficiency of t h e preparation, therefore, resides largely in i t s fine s t a t e of subdivision a n d care must be t a k e n during t h e process of preparation not t o expose i t t o air until after thorough digestion with alcohol of 90 per cent strength. After drying i t should be preserved from moist air, though i t is not injured b y exposure t o ordinary atmospheric conditions. T h e advantages of t h e material for iodine titrations made in t h e field with a portable outfit are sufficiently obvious. It id also a very convenient substance t o have a b o u t a laboratory, although for highly accurate titrations it is somewhat inferior in sensitiveness a n d delicacy t o a properly prepared fresh solution made from r a w starch. Since t h e above described process was worked o u t , Fernbach' has described very similar observations; namely, t h a t a dilute starch paste or solution r u n in a fine stream into a large excess of absolute alcohol or acetone, produces a finely divided precipitate a-hich is soluble in cold water. H e apparently a t t r i b u t e s t h e soluble qualities of t h e resulting product t o t h e dehydrating action of t h e alcohol or acetqne. Inasmuch as t h e horny form of precipitated starch previously mentioned, a n d indeed r a w starch as well, becomes soluble in cold water when finely ground, t h e present writer believes t h a t t h e prime factor which determines t h e readiness with which precipitated starch dissolves in water is simply t h e degree of fineness of i t s mechanical subdivision. It was early found t h a t t h e more dilute t h e original starch solution a n d t h e greater t h e excess of alcohol, t h e finer, more voluminous a n d more readily soluble in water became t h e resulting product, b u t n a t urally, t h e less practical became t h e process. BIOCHEMIC DIVISION, BUREAUO F ANIMALI N D U S T R Y s. DEPARTMENT O F AGRICULTURE, W A S H I N G T O N
u
Ongrnal Communicatrons, Eighth International Congress of A p p l r e d Chemistry. 13 (1912). 131. 1
Vol. 6 , No. 8
DETERMINATION OF SILVER AND BASE METAL IN PRECIOUS METAL BULLION' By FREDERIC P. D E W E Y ~ Received May 15. 1914
T h e determination of silver in gold bullion b y cupellation methods is such a simple m a t t e r a n d so easily executed t h a t i t has long been t h e s t a n d a r d a n d almost universally accepted method, b u t t h e investigations described in this paper show t h a t i t has most serious a n d incurable defects. I n making a n assay of gold bullion for base metal, which is t h e basis for t h e silver determination, t h e base metal is n o t entirely removed f r o m t h e b u t t o n , a n d n o means are a t present available f o r insuring t h e presence of even approximately t h e same a m o u n t of remaining base metals in duplicate buttons. T h e judgment of t h e cupeller is t h e only guide in t h e matter. T h e a m o u n t of gold a n d silver absorbed b y t h e cupel m a y v a r y greatly in duplicates. T h e proofs are subject t o t h e same variations as t h e assays, a n d i t is purely a m a t t e r of chance whether t h e y give t h e proper correction figures or n o t , a n d t h e y m a y fall f a r short of doing so. These difficulties are inherent in t h e work of a n y one assayer, b u t when different assayers work upon t h e same sample, particularly in different laboratories, t h e opportunities for variation are multiplied; when t h e y work upon different samples of t h e same bullion, there is n o telling how widely they m a y differ in their reports, even upon apparently docile bullion. There is urgent need for a better method, b u t a thoroughly better one is not yet available a n d undoubtedly t h e cupellation method will remain in use for m a n y years t o come. This paper further describes a n a t t e m p t t o establish a better method b y means of fusion with cadmium a n d titration with sulfocyanate, which, while not entirely successful, is very promising. Comparative tests b y cadmium fusion a n d Gay-Lussac titrations are also described. During t h e fiscal year ended June 30, 1912,t h e M i n t service of t h e United States Treasury purchased 7 4 , 1 j 9 deposits a n d redeposits of bullion, most of which contained more or less silver. I n t h e vest majority of cases t h e fineness of t h e silver i n t h e bars was not determined directly, b u t b y a method of differences based upon cupellations b y which t h e fineness of gold a n d base metal present were determined, t h e difference between these t w o actual determinations a n d 1000 being called t h e silver fineness. There are two general methods of arriving a t t h e silver result. T h e actual assaying work in both cases is t h e same, b u t t h e methods of calculzting t h e results differ. I n both of t h e m t h e gold fineness is first determined b y a separate assay. T h e n , in one method of calculating, t h e combined gold a n d silver fineness are determined by a second assay a n d t h e gold figure subtracted from t h e combined gold a n d silver figure t o give t h e silver fineness. I n t h e second method of calculating, t h e result of t h e second cupellation is s t a t e d as t h e loss on cupellation, or base metal, a n d t h e s u m of this determination a n d t h e gold determination is subtracted from 1000 t o give t h e silver fineness. 1
4
Published by permission of the Director of the Mint. Assayer, Bureau of the Mint.
