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the electrical conductivity of boric acid is increased more or less by a considerable number of polyhydroxy organic compounds, but it is evident that they are not necessarily of value, therefore, for use in determining boric acid. The action of the hydroxy acids already mentioned indicates that they are not of value. A number of the other compounds showing only small effects upon the position of the curve might be of value if used in sufficient quantities. This is true, of course, for glycerol. Later work may show also that some combination of polyhydroxy organic compound with an inorganic salt is effective. The curves bearing upon this point are presented merely as preliminary observations. The substances which should be suitable for use include manna, mannitol, sorbitol, dulcitol, fructose, and invert
Vol. 16, No. 2
sugar. Of this list sorbitol, dulcitol, and fructose are too expensive for extensive use, leaving for consideration mannitol, manna, and invert sugar. The curve for mannitol has the longest vertical portion, indicating that it is the most effective substance for the proportions used. Both manna and invert sugar give curves lying close to that for mannitol. Their vertical portion is shorter but properly located for a satisfactory volumetric determination of boric acid, using either of these substances along with phenolphthalein or cresol red as an indicator. Several determinations were made in this way in order to check the accuracy of such a conclusion. According to the prevailing price of chemicals, invert sugar is the cheapest material to use, although preparation of a solution of it involves more time than weighing mannitol or manna directly. 1
A n Inexpensive Laboratory AMilll>z Designed for the Grinding of Dried Fruits and Similar Materials in the Presence of a Liquid By R. Adams Dutcher and John F. Laudig PENNSYLVANIA STATECOLLEGE,STATECOLLEGE, Pi.
HE mill described herein is the result of experiments to design % machine for grinding raisins, dried fruit, and in the presence Of Other similar water or other solvent. The apparatus was originally designed to assist buyers of dried grapes in ascertaining the sugar content of the product they were buying, but the writers believe that the mill could be used in a variety of ways in most laboratories, especially in the preparation of colloidal materials and in the grinding of many agricultural, biological, and pharmaceutical materials. This mill was constructed in the college shops at a cost of about $30.00. I n order to obtain the information necessary for properly classifying the dried fruit, the sugar content must be estimated while the shipment is being unloaded and graded, which requires about twenty minutes, The method described in this paper gives fairly accurate results on the determination of the sugar content of dried raisins in a very short time, even in the hands of a nontechnical worker.
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1-Gummy materials had t o be ground in the presence of a solvent t o remove the sugars as rapidly as possible from the tissues. 2-The material had t o be ground t o a very fine state of subdivision t o insure complete solution of the sugars present. 3-The mill had t o be so constructed that no material could be lost during the grinding process. 4-It was also essential t h a t the mill be easily and quickly and r e a ~ m ~ b l e d .
DESIGN I n designing the mill shown in Figs. 1 to 4, the following conditions had to be met: 1 Presented before the Division of Agricultural and Food Chemistry a t the 66th Meeting of the American Chemical Society, Milwaukee, Wis., September 10 to 14, 1923. Published as Contribution No. 5 of the Department of Agricultural Chemistry, Pennsylvania State College.
*
FIG.1-A
CROSS SGCTION O F THE MILL SHOWING DISKS, ADJUSTING MECHANISM, RECEIVING CUPS,A N D DRIVINGSHAFT
Fig. 1 shows a cross section of the mill as finally built. It consists primarily of two steel disks 4l/2 inches in diameter, the upper one being stationary while the lower one is rotated a t a speed of 1200 to 2000 r. p. m. according to conditions. In each disk are cut several channels with their cutting edges so arranged that there is a shearing action between the disks. The channels are deep (about '/IB inch) at the center and practically disappear at the periphery. The surfaces of the disks slant downward away from the center (at an angle of about 5 degrees) so that the larger particles will be drawn down by gravity and pass between the plates. The lower disk is connected to the driving motor by means of a 1/4-inchleather belt. The receiving cup is made of tin and is inches in diameter and 5 inches high. The bottom of the cup is conical and made so that it fits snugly over the shaft. casing below but not touching the lower disk, as shown in Fig. 1. The interior surface of the cup is perfectly smooth, any crevices
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INDUSTRIAL A S D ENGINEERIAVGCUEMlMTRY
February, 1921
being filled with solder. This facilitates cleaning. The re. ceiving cup and lower disk are removable and the upper disk is held in place by a hinged crosspiece on the frame. a n adjnsting nut at the top of the stationary disk permits regulation of t.he distance between the plates, and a strong spiral spring imparts the necessary pressure to thc grinding surfaces. The framcwork is constructed of wood 3 inches thick, except for the hinged member carrying the upper disk. which is inches t,hCck. When assembled the mill and frame are 17l/4 inches thick and 25 inches lone. (Figs. 2, 3, and 4.) The upper disk is screwed on to a piece of 1-inch pipe, which provides means for both mounting the disk and charging the mill. The finely ground material is whirled from the rotor to dlie receiving cup, from which it can he drawn off through the the particles in the origidrain pipe to n beaker or flask. If nal material are large, it is advisable to adjust the disks some distance apart at first and pass the suspension through several times, hringing the disks closer together after each pass. By this treatment a very fine suspension can be ob-
127
per. A 50-gvst.te sample of the ground material is suspended in about 200 cc. of boiling water and passed through the mill as many times as neeessary. In tk.3 case of raisins three times will umally suffce. The disks and receiving cup are then washedwith successive additions of warm water while the mill is running,.until all materials are washed into the receiving beaker or flask. The suspension and washings are cooled in running water and made up to 500 cc. volume a t 20” C. If analyses are not to hc made immediattly, four or five d r o p of iiilueir ihould hc added to prevent the dwelopment of moldi
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tained in a surprisingly short time. The resulting suspension can then be subjected to any analytical procedure desired.
DETERMINATION OF RAI~IN SUGARS To insure uniform sampling and facilitate grinding, ahout 200 grams of raisins are passed through an ordinary food chop-
The srmicentemiial of the organization of La Societb FranEnise de Physique was cclebrated in Paris, Dccember 10 t o 15, by a series of lectures by distinguishcd physicists given in the Amphitheatre de Physique a t thc Sorbonne, and by other functions. The most interesting lecturer were by Loreriz on “The New Mechanics:” Lord Rayleigh on “Iridescence;” Stormcr on “The Aurora Borealis;” and by Knudseii oil “The Mechanism of Evaporation and Condensation.” On Wednesday eveninp, the lZth, there was an elegant banquet a t which several hundred physicists from the principal couiitries of Europe were present. Thursday aitemoon, the 13tl1, there was a ”Sbance Solennelle” i n , the Grand Amphitheatre 0% the Sorbonne, with Alerandre Mdlerand, President of the Republic, in the chair. On this occasion, in addition to addresser on the history of the society, there was an address by Charles Fabry on “Explorations in the Field of Radiation.” An exposition oi physics in the Grand Palais, which was oripinally planned to last for two weeks, proved to be so popular that it was continued for a third week. The exposition contained both scientific and commercial exhibits from all fields of physics. the exhibition oi electrical apparatus being especially prominent. The entertainment of delegates t o t h k celebration was provided for with true French hospitality.-W. A. NVYES
