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INDUSTRIAL
AND ENGINEERING
Electroplaters' and Depositors' Technical Society A t a meeting of this Society held in London o n November 9, 1S27, E. A. Ollard presented a paper advancing a new theory of the electrodeposition of chromium.
CHEMISTRY
News
terial and regulates the acidity, the chromic bichromate forms a buffer substance and reduces acidity, and t h e chromic salt pro vides the supply of chromic i o n s from which the deposit of the metal takes place. Some colloidal matter may be formed on the cathode and may affect t t i e structure of t h e deposit, but there does not appear t o b e a n y great quantity of such material in the body of the solution.
N E W THEORY O F CHROMIUM PLATING
Mr. Ollard, in the course of his remarks, said that, so far, three theories had been put forward to account for the working of the chromium bath. The first of these seems t o be chiefly held b y the American workers. This is to t h e effect that t h e deposition of the chromium takes place from the small percentage of chromium sulfate (or other salt) in the bath, and that the chromic acid functions a s a reservoir from which the chromium can be drawn. They appear to consider that the chromium sulfate electrolyzes to give chromium and a sulfate ion, which reacts with the chromic acid, regenerating chromic sulfate. The chief objection to this theory is that there is no evidence that a sulfate ion would react with chromic acid, or if it did that it would form chromic sulfate; moreover, the theory does not make it clear why better results should not be expected from chromic salts alone. Doctor Liebreich, studying the current-voltage curves a t a platinum cathode in chromic acid solutions, concluded that the deposits of chromium took place in steps from t h e chromic acid itself, the hexavalent chromium being reduced by the current first to tri valent and then the divalent step, and finally the metal. His theory does not explain why pure chromic acid should not also give deposits of chromium, or the function of the addi tions of other acids. He has, however, produced considerable evidence t o show that divalent chromium compounds are formed prior to the deposition of the metal. Doctor Muller has endeavored t o explain t h e action of the sulfuric acid by a complicated theory of colloidal diaphragms. He suggests that the chromic acid is reduced at the cathode by the nascent hydrogen, but that the reaction is stopped immedi ately by the formation of a semipermeable membrane of chromic ehromate produced from the reduction products, allowing only hydrogen to pass through it. He further suggests that the addi tion of another acid modifies the diaphragm and allows the reac tion to proceed. From conductivity tests, potentiometric measurements, mi gration tests, and chemical analyses, it w a s considered that the solution must consist essentially of the following constituents, in order that deposits of chromium m a y be obtained from it : (1) Bichromie acid—usually in fairly large quantities, but may be re duced almost to zero. (2) Bichromate of chromium [CnCCraCMsl—from nearly zero to a very large percentage, varying inversely as the amount of bichromie acid. (3) A substance that will give another anion, a s sulfuric acid or a sulfate— a small quantity only, which has to be very carefully controlled and varies with the type of bath used and the material itself. (4) A complex colloidal compound of chromium of type CnOa.xCrOj, where χ is lew. Colloids of this description are found but do not appear t o be present in large quantities, and there is n o evidence that they are beneficial.
The first two constituents are obtained by dissolving chromic trioxide in water and reducing to the desired degree by a con venient method. T h e third constituent i s carefully added in the required amounts, although in some cases part of this m a y be present a s an impurity in the chromic trioxide and allowance must be made for it. The existence of t h e fourth constituent is doubtful, but if present it m a y be formed either during the re duction of the chromium trioxide or by subsequent electrolysis. T h e last suggestion is probably correct, a n d it is found that col loids can be experimentally produced in t h i s wayI t is not considered possible that in a bath of this nature any divalent material could exist in the bulk of the solution while at rest. The composition of the solution must therefore be con sidered as being bichromie acid and chromic bichromate, together with a small quantity of chromic sulfate (or other salt). The concentration of the trivalent ions will be governed b y this last constituent, since the chromic bichromate as shown above ionizes only slightly and will therefore serve as a buffer substance. From a careful consideration of all tlie available data the mechanism of the reaction was considered to b e as follows: In the body of the solution trivalent chromium compounds, usually the sulfate, ionize t o give a trivalent ion. When current is passed the bichromie acid functions as a conducting material, and the chromic ion is carried to the cathode. The bichromie acid will be electrolyzed, forming oxygen and hydrogen, while the chromic salt will give a chromic ion at t h e cathode and the ion of the corresponding radical at the anode, which will react with chromic bichromate, re-forming t h e salt and bichromie acid. T h e chromic ion will be reduced a t the cathode, forming first a chromous ion and then the metal. Some of t h e chromous ions formed may, however, escape from the cathode layer, reacting with the bichromie acid to form further quantities of t h e chromic bichromate. Thus t h e bichromie acid forms the conducting ma
Edition
S. WERNICK 3 BRIDGE ST., E. 3 LONDON, ENGLAND
T h e Synthesis of Lactose BY G E O . W \
MUHLEMAN
Hamline University, St. Paul, Minn. (In residence at: Geneva 1926-27)
The writer has been g i v e n permission by Amé Pictet, professor and director of inorganic and organic chemistry, Ecole de Chimie, the University of Geneva, to announce through t h e columns of t h e N E W S E D I T I O N of I N D U S T R I A L AND ENGINEERING CHEMISTRY
the successful synthesis of lactose. On December 16, 1927, "Doctor Pictet, in a very brief report before L e Société des Sciences Physiques et Naturelles, announced his accomplishments and gave the reactions involved in the synthesis. They are as follows: β-galactose (C6H12O6) yields β-galactosone a n d water, one molecule of each. One molecule of β-galactosone reacts with one molecule of β-glucose to yield one molecule of lactose. Doctor Pictet requested that the writer delay making this report in America until he had still further checked u p his results so t h a t the announcement might not be premature. A full report of the accomplishment has been printed [Helv. Chim. Acta, 11, 209 (1928)]. Doctor Pictet's first w o r k of note w a s with the alkaloids. He synthesized nicotine, papaverine, laudanosinc, berberine. A comprehensive description of t h i s work may be found in Woolffanstein's "Die Alkaloide." From 1910 to 1914 Doctor Pictet studied the decomposition products of coal, wood, and cellulose in high vacuum and at high temperatures. He found that the hydrocarbons were entirely different from those produced by the ordinary destructive distillation of coal by utilities com panies. This idea was e m p l o y e d by the German chemists, with some modifications, in synthesizing motor fuel from coal. Doctor Pictet dehydrated cellulose and starch, at high temperatures and in high vacuum and was able t o secure a yield of from 2 5 to 30 per cent of anhydrous sugar. The task of synthesizing disaccharides has engaged Doctor Pictet's time and energy since 1914. Sugar chemists are able t o appreciate the many insurmountable difficulties accompany ing such an undertaking and axe happy t o unite in extending congratulations to Doctor Pictet at this, h i s latest and greatest achievement.
Charles M. Hall Research I n s t r u c t o r s h i p In honor of Charles M . Hall, the brilliant Oberlin alumnus who. in 1886, discovered the modern process of producing the metal aluminum, Oberlin College h a s founded a research instructorship. A young man w h o has recently taken his Ph.D. degree and who has some interest b u t little or n o experience in teaching is appointed research, instructor for one year only a t $2000. Three-fourths of his t i m e is spent i n cooperative research on colloid problems with H a r r y N. Holmes, and the remainder as a teaching apprentice to t i e entire staff. Thus h e learns whether he likes the teaching field or is qualified for it. H e gets a training in colloid chemistry a n d a joint publication may result. Furthermore, he has such teach-ing prestige as the title of instruc tor gives. This is an example for other colleges. College faculties need to encourage their members t o continue in research b u t , as a matter of fact, most of these institutions (we are not including graduate schools) discourage research by overloading the pro ductive type of teacher with routine duties. Aided b y fellows or research instructors a college professor may accomplish much more in research than if left unaided. The above plan will attract men to the teaching profession and hold them in it*
Table of Preferred N u m b e r s The American Bngineering Standards Committee, 29 W. 39th St., N e w York, Ν . Y., h a s recently issued a table of pre ferred numbers which is being recommended to American industry for trial and criticism. A ne j>urpusc of t h e system is t o elimi nate the economic loss involve*! in t b e haphazard gradations of size that characterize most c o m m o n commodities. Copies of the tabie may be had
