INDUSTRIAL AND ENGINEERING CHEMISTRY
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If possible contamination with copper were objectionable, the condenser could be made of some other metal or of glass. A form of glass condenser which was tried is shown on the right (Figure 1). A thin-walled tube, closed at one end, is fused at its open end to the bottom of a larger tube, which should have as thin walls as is consistent with the desired mechanical strength. An ordinary funnel inverted over the top of the inner cylinder completes this set-up, the stem conducting the vapor into the inner tube of the condenser and the funnel itself diverting the returning solvent to the space between the two cylinders of the extractor. The condenser is supported by a clamp, and is provided with cooling water tubes through a stopper. Although the glass condenser functions fairly well, a metal one is more satisfactory where permissible. Because of the more rapid transfer of heat, the metal condenser may be made shorter, thereby avoiding undesirable length in the outer cylinder. Before filling the extractor, cotton is placed in the bottom of the outer cylinder to act both as a filter and as a cushion for the inner cylinder. More cotton may be placed in the bottom of the inner cylinder after i t is in place, if desired, to distribute the solvent better through the meal. During filling, the center tube may be protected by a cork or cotton plug or b y a short piece from the bottom of a test tube. The weight of the inner cylinder and its contents compresses the cotton filter and adds unnecessarily to the head
required to maintain a flow of solvent. There are several ways of eliminating this resistance t o flow: small holes may be made in the inner cylinder as near as possible t o its bottom edge; washed and ignited sand may be placed in the bottom of the outer cylinder before the cotton is put in; or the inner cylinder may rest on indentations made in the outer cylinder (X, Figure 1) instead of on the cotton. The depth of material to be extracted is governed mostly by the depth of solvent required above it for settling of the finer particles of the solid. If necessary, when there is a n interest in the extract as well as in obtaining fat-free meal, a cotton plug may be placed above the solid material being extracted, to act as a filter. Since the maximum obtainable head of liquid is fixed by the difference in level between the top of the solvent vapor tube and the top of the inner cylinder, i t may sometimes be necessary to reduce the depth of the material being extracted to insure adequate flow of solvent. However, this difficulty has not been encountered in the extractions attempted. A head of 10 em. (4 inches) gave ample margin for the extraction of about 20 em. (8 inches) of cottonseed meal. RIGCEIYED July 11, 1934.
A Hot-Water Funnel
A Rapid Method for Making Standard Solutions of
JOHNR. CALDWELL Ohio State University, Columbus, Ohio
Specified Normality OTTO JOHNSON State College of Washington, Pullman, Wash.
C
ONSIDERABLE loss of time may be averted in the preparation of standard solutions of exactly specified normality by the use of the method outlined below. EXAMPLE: Prepare 18 liters of an 0.1142 N solution of sulfuric
acid: 1. Calculate its equivalent in terms of a normal solution: 18 X 0.1142 = 2055.6 ml. of normal solution.
VoI. 7, No. 1
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HE sketch shows the design of an easily constructed hot-water funnel. The container, A , is made b y
cutting the top from 8 bottle of convenient size. The side tube, B, may be constructed of glass or copper tubing, and should be 8 to 10 mm. in diameter to insure rapid circulation. The model shown is designed for heating with a Bunsen burner, but a resistance coil may be wound on the side tube for electrical heating.
2. Prepare about 1100 ml. of an approximately 2 N solution
of sulfuric acid. From (1) it is evident that about 1028 ml. of this solution are equivalent t o 18 liters of 0.1142 N solution. 3. Into approximately 17 liters of water measure accurately about 1000 ml. of the 2 N acid, so that the standard solution is
less than the desired normality. If the normality is greater than the desired value, dilute with water but do not discard any solution. 4. Determine the normality of the above solution. For purposes of illustration assume that it is found to be 0.1109 N . 5. From these data it is ossible to calculate exactly the number of milliliters of the 2 $solution required for this volume of standard solution by means of the equation 1000:~::0,1109: 0.1142 from which z = 1030. This represents the total number of milliliters of 2 N solution required t o make the standard solution exactly 0.1142 N and when the additional 30 ml. of 2 N solution are added the final determination of normslity may be made This procedure will be found less laborious than the CUStomary one of making the solution stronger than desired and-then diluting with water. The accuracy depends upon the care with which the first determination of normality is carried out, since 1 ml. of the 2 N acid makes a difference of only slightly more than one in the fourth place in the particular example cited. When the work is done carefully the final determination of normality need serve only as a check and rigorous adherence to this procedure will be found to result jr an economy of both time and effort. R E C E I V ~September D 22, 1934.
The design is easily adapted to any size, and lends itself readily for use in semi-microwork where very small apparatus is essential. Biichner funnels as well as the 60' glass funnels may be accommodated. A few grams of salt dissolved in the water will raise the temperature of the bath so that, when aqueous solutions are filtered, they are maintained at the boiling point. It is recommended that the rubber stopper be wired-in place. RECBXVED October 17, 1934.
