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
580
reducing the molybdenum by the rotating zinc cylinder (no electrolytic current) and then pouring the reduced solution into a beaker containing ferric alum and phosphoric acid (2 j cc. ferric alum solution, made by dissolving IOO g. ferric alum in I liter ot water; j cc. sirupy phosphoric acid). TABLEI V MOO8
Taken G. 0.0815 0.0818 0.0816 0.0819 0.0816 0.0815 0.0814
Moos
Found by
KMn04 0.0818 0.0818 0.0811 0.0812 0.0814 0.0815 0.0810
Error G. 4-0.0003 0.0000 -0.0005 -0.0007 -0.0002 0.0000 -0.0004
Time of Temp. Vol. at Reduc- before Titrstion Reduction tion Min. O C. cc. 5.5 5.5 5.5 5.5 5.5 5.5
5.5
25 30 23 22 22 21 22
400 400 400 400 400 400 400
Rev. per Min. 700 700
700
700 700
700 ,700
The above results show t h a t the reduced molybdenum solution may be titrated in a separate beaker from t h a t in which i t was reduced, provided the mixture of ferric alum and sirupy phosphoric acid is used to effect t h e preliminary oxidation of the molybdenum while in the very sensitive stage.
Vol.
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No. 6
desired. A situation arose a t this plant not long a g o demanding t h a t the arsenic content of each shipment of acid be determined before the shipment was received. The literature on this subject was accordingly examined, and various methods tried, but all proved: laborious and time-consuming. Some of t h e methods involved the reduction of t h e arsenic in the arsenic form, some a precipitation with hydrogen sulfide, and some both of these procedures. T h e ones giving t h e best results were t h e most time-consuming, t h e operation requiring t h e greatest amount of time being t h e reduction of the arsenic form. I t was thought, accordingly, t h a t a method involving t h e determination of e&ch form of arsenic separately would be very advantageous. The determination of arsenious arsenic presented no particular difficulty, as a slight modification of one of the standard methods would suffice. T h e method for the determination of each form finally adopted is given below.
CONCLUSIONS
The foregoing results show t h a t molybdic acid in dilute sulfuric acid solution may be reduced by a rotating zinc cylinder, either with or without the aid of the electrolytic current, when certain precautions have been observed; also t h a t when ferric alum a n d sirupy phosphoric acid are added immediately t o t h e reduced molybdenum solution, t h e titration may be made in a separate beaker from t h a t in which reduction is brought about. The molybdic acid may be determined quantitatively in all cases by titrating the reduced solution with standard potassium permanganate. The above processes may be advantageously used in place of the ordinary Jones reductor, after interfering substances have been previously removed by any of t h e ordinary methods. Assuming ammonium phosphomolybdate t o have the composition ("4)sP04.12Mo03, P or PzOs may be indirectly determined by this method. I t might also be added t h a t when t h e work on this series of articles terminated, t h e writer was working on a volumetric method for the determination of tungsten (or tungsten trioxide) and had succeeded in keeping it completely in solution practically t o t h e W 0 2 stage. This process will be further investigated a t some future time. ACKNOWLEDGMENT
This work was done in the Kent Chemical Laboratory of Yale University in 1916, and the writer wishes t o thank Professor F. A. Gooch, whose interest was stimulating and kindly advice most helpful a t all times. A RAPID METHOD FOR QUANTITATIVE DETERMINATION OF ARSENIC IN COMMERCIAL SULFURIC ACID By A. A. Kohr SEABOARD BY-PRODUCT COKECo.,JERST~Y CITY,N. J. Received January 29, 1920
I n various commercial operations where sulfuric acid is used, an acid of low arsenic content is often
METHOD
A R S E N I O U S FORM-weigh o u t 2 0 g. of acid and dilute with a small amount of distilled water, and add a f e w drops of methyl orange indicator. Carefully neutralize with a saturated solution of sodium carbonate until t h e methyl orange shows a very faint pink (about o n e drop more would t u r n the solution completely yellow), and add about 2 g. of sodium *bicarbonate powder in excess. Make up solution t o about 2 5 0 cc. with distilled water, if necessary, and titrate with 0.1 N iodine solution, using starch as a n indicator. A blank determination should be made on the reagents and suitable correction made. Cc. 0.1 N iodine X 0.004gj = g. As203 in t h e arsenious form. ARSENIC FORM-weigh out 2 0 g. of the acid t o b e tested into a small beaker, and place in a n oven regulated a t ~ o j 't o 110' C. for about a n hour. Dilute with a small amount of distilled water, and add a. saturated solution of sodium carbonate until just in excess (red color with phenolphthalein). Boil, and: filter into an Erlenmeyer flask. Wash thoroughly a n d add about 3 g. sodium bicarbonate powder, add 1 5 0 cc. strong hydrochloric acid slowly with occasional agitation, then add about I g. potassium iodide crystals, and cover the flask t o keep out air. Agitate and then allow t o stand j min. Titrate the iodine liberated with 0.1N thiosulfate, with starch as indicator. Cc. 0.1 N thiosulfate X 0.004gj = g. As203 i n arsenic form. Arsenic in arsenic form arsenic in arsenious. form = total Asi03. Total As20s X j = per cent total AszOa. Per cent total AszOs x 0.757 j = per cent total As.
+
DISCUSSION
+ +
+
H ~ A s O ~ 2HI HaAsOs I2 HzO The above reaction proceeds from left t o right whern t h e hydrogen-ion concentration is low, and there.
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T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
should be very few OH ions. Excess sodium bicarbonate does not interfere. I n the presence of sufficient hydrochloric a d d t h e reaction goes from right t o left. It is quantitative in both directions. Salts of copper interfere in t h e above determination of t h e arsenic form of arsenic, but in most cases t h e copper content will be low enough t o be negligible. Should. copper be found in a n appreciable quantity, however, it should be determined and a correction applied t o t h e thiosulfate titration, remembering t h a t each mole of copper will liberate one mole of iodine from potassium iodide. If copper is present in any
quantity t h e amount of potassium iodide added should be increased accordingly. The only other constituents likely t o interfere with the determination of the arsenic form have been removed by t h e method of procedure. Nitrous and nitric acids would be volatilized during the heating. Ferric iron would be precipitated by the sodium carbonate and removed in the subsequent filtration. This method has been checked against various other arsenic methods and results have been found t o agree very well. Duplicate determinations of t h e same acid have been found t o check closely.
LABORATORY AND PLANT SEED-CULTURE METHODS IN THE PRODUCTION O F ACETONE AND BUTYL ALCOHOL BY A FERMENTATION PROCESS
By Horace B. Speakman DEPARTMENT OF
ZYMOLOGY,
TORONTO U N I V E R S I T Y , TORONTO, CANADA
Received January 15, 1920
A bacteriological fermentation process may be divided for descriptive purposes into two parts: firstly, t h e preparation, fermentation, and distillation of the large bulk of raw material; and secondly, the preparation, in an active and pure condition, of the necessary volume of culture, t o act as seed-culture for t h e final fermentation. I n a previous article' a n outline was given of t h e essential features of a plant concerned in t h e first of these divisions of t h e process. I n t h e present communication it is proposed t o consider the apparatus and methods of working in t h e production of seed. Emphasis must be laid in the first place on the necessity of a n adequately equipped laboratory. Furthermore, t h e principles of bacteriology must be allowed t o control and direct not only t h e laboratory, b u t the operations of t h e entire plant. The problem consisted in finding the best method of developing from a laboratory tube culture a sufficiently large and active volume of culture t o start a fermentation in a large fermenter, containing 24,000 gal. of mash, which will occupy t h e minimum number of hours and give t h e maximum yield of products. Such questions as t h e following a t once arose: ( I ) What is the correct ratio between the volumes of the seed-culture and t h e mash t o be inoculated? ( 2 ) At what stage in the fermentation must t h e cult u r e be used as seed? ( 3 ) Can t h e organism growing in maize mash be subcultured indefinitely in the same t y p e of medium without loss of vitality? If not, what is t h e number of generations between t h e tube and t h e fermenter which will insure t h e maximum efficiency in t h e 1a t t er 7 Because t h e great demand for acetone made impossible small-scale, preliminary experiments, these ques1
Speakman, J . Sac. Chem. I n d . , 38 (1919), 155.
tions were answered in t h e factory rather t h a n in the laboratory. The seed plant was often modified, and, when t h e armistice was signed, it represented the sum of the experience gained during the previous two and a half years. The second question will be considered in detail. During t h e fermentation the acidity of t h e mash rises steadily for about 1 5 hrs. and then falls for about the same number of hours. I n all stages of t h e seed process t h e culture was transferred t o the next batch when t h e acidity had just begun t o fall, for the following reasons: At this point the organism had ceased dividing and had passed through the chain stage. The medium, however, had not yet separated into a clear fluid with a slimy floating head which contained t h e majority of t h e bacteria, b u t was still homogeneous and contained t h e maximum number of free motile organisms. I n this condition the culture could be divided equitably between several batches of mash. I t was also found t h a t when contamination occurred only one species of foreign organism developed, and this type was responsible for t h e stoppage of the fermentation. I n t h e early stages t h e contamination could not be detected by its morphology or b y chemical tests, b u t toward t h e end of the fermentation t h e contamination stood out clearly in faintly stained preparations, and t h e acidity of t h e mash did not fall but rose t o a very abnormal maximum. For these reasons i t was considered advisable t o wait until t h e acidity had commenced t o fall, and until slides had been examined very carefully, before passing t h e culture into a larger volume of mash. A further question arises in connection with the number of vessels t o be included in the system. Supposing t h a t 1,000 gal. of culture are required each day for four large fermenters, is i t advisable t o prepare this in one or more vessels? If one vessel is used there is a saving in time and labor, and, what is of greater importance, b y reducing t h e number of pieces of apparatus t o t h e minimum t h e danger of contamination is correspondingly reduced. On the other hand, if contamination does occur, the plant may be idle for a day. Furthermore, whilein general it is possible t o arrange t h a t the culture be in the right condition when required, occa-
