V O L U M E 19, NO. 1 0
812
part of the distilling flask and evaporated to dryness on its overheated surface. Consequently, in spite of the fact that antimonious chloride does not volatilize in an aqueous hydrochloric acid solution, its real vapor is formed and carried with the outgoing vapor stream. The liquid condensed in the interior of the. droplet’ catcher is sufficient i o dissolve this antimonious chloride and carry it back to the boiling solution. The passing of a stream of hydrochloric acid through the liquid and the use of any of tht. other precautions formerly suggested for this purpose arc thus eliminated and a sharp separation of arsenic and antimony can be performed in a single distillation. h former model of the device described ( 1 ) had an inner steam conducting tube which did not affect the efficiency of the droplet catcher, but causrd difficulty in filling it with the small glaFs rings. So, although highly appreciat,ed by the chemists who used it, the device has not been fabricated in quantity. The new modificat.ion overconies thew technical difficulties in the fahrication. ’
TESTISC, EFFICIENCY O F DROPLET CATCHER
I n a 1-liter flask provided with a connecting bulb 500 ml. of 1 -I’sodium hydroxide and a small quantity of zinc powder (to generate hydrogen) were boiled. The pH of the distillate was found to be 8 to 9, proving that one part of dispersed liquid was carried along with 100,000 to 1,000,000 parts of distilling liquid. When the assay was repeated, the interior droplet catcher replacing the exterior bulb, the p H of the distillate \vas 7.0 to 7.2. At the same time, if the position of the distilling flask and the height of the gas flame were maint’ained exactly, the distilling rate, in milliliters per minute, increased 50%. It could have been further improved up to 100% by increasing the intensity of heating. On the other hand, when the connecting bulb was used, it ivas not possible to speed the distillation by more intense boiling because in this case the condensed liquid closed the inner tube, so that the passing steam threw quantities of it towards the condenser. Exactly the same relations were observed in the distillation of an acid ammonium chloride solution with zinc powder and measurement of the ammonia in the distillate iTith Kessler reagent; no coloration a t all \vas found with the droplet catcher, while 10-6 t o part of the ammonia content of the boiling liquid was observed in the distillate when the conventional connecting ,bulb via3 used. -in example may be cited as nonanalytical proof of the efficiency of the droplet catcher. I n 1942, while in charge of a n agricultural
Figu
1.
Droplet (:atc*her
institute, where it was not possible to acquire a modern still, the, author was in immediate need of reIat,ively large quantities of distilled water, pure enough t o be used in soil analysis. d n oltl still of some 30-liter capacit,y, regarded as unserviceable, wai found in storage. A droplet catcher was installed in the interioi. of the ret,ort and the still 17-as fed with tap water to which potassium permanganat,e and sodium hydroxide were added continuously. During two years, the outgoing distilled water x a > always colorless and practically neutral. I n this case the uw of the droplet, catcher proved that it, is possible to obtain n-atcbi, with the purity of “redistilled” water in a single distillation. LITERATURE CITED
(1) Hahn, F . L., Ber., 57, 1858 (1924). RECEIVED October 23, 1946
Apparatus for Rapid Electrometric Titration of Acid Determination of p H and Measurement of Turbidity in Microbiological Assays I.0UIS B. ROCKL,IND
AND
3IAX S. DCNN
Chemical Laboratory, Cnicersity of California, Los Angeles, Calif.
apparatus shown in Figure 1 has been employed more than a year in the writers’ laboratory for the determination of turbidity, pH, and titratable acid of solutions in the microbiological assay of amino acids and vitamins. These measurements may be made simultaneously by an experienced worker with the aid of a technician at the rate of about 90 per hour and independently a t rates of about 150, 300, and 200 per hour for turbidity, pIi, and titratable acid, respectively. Reeves ( 2 ) has described an apparatus for multiple p H determinations and Silber and Nushett ( 5 ) have pointed out the convenience, speed, objectivity, and applicability of the p H procedure in the determination of pantothenic acid with Lactobacillus casei. A spread of about 2 pH units was obtained over a working range of 0.02 to 0.10 microgram of pantothenic acid per tube. The precision and accuracy attained by the present authors in microbiological assays of histidine with Leuconosfoc mesenteroides P-63
have been reported ( 1 ) . I t has been found that the acid produc,tion of organisms in microbiological a s s a y may be deterniinc~tl more rapidly, conveniently, and accurately by means of the dcxscribed apparatus than by titration using bromothymol blue indicator to determine the end point. Some of the shortcomingwhich are eliminated or minimized include eyestrain, general fatigue, and end-point errors caused by indicator fading, turbitlity, and colorations. ’ APPARATUS
The titration cup is a Pyres funnel, -4 (Corning 6110, ESPGY , and 2- to 3-mm. bore Pyres stopcock, b. The outlet, a , of the cui) under stopcock b is clamped to a ringstand and is connected to :L water aspirator with rubber pressure tubing. A 25-m1. automatic zero Kimble Blue Line Exax buret, B , with a three-way stopcock is clamped t o the ringstand in such a mannc-i’ that the buret is just above and in the center of the titration cup.
OCTOBER 1947
813
oi the 5topcock by gravit). bon dioxide-free base. .in .k.i,ii-\Iix ~ l ' r ~ ~ i s i ~ i r i ompany) stirrer, C, is iit slightly to effect rapid mising of thv liquidj
