ISDUSTRIAL AVO E,VGIhTEERING CHEMISTRY
March, 192.5
dissolved copper. After standing 48 hours, it was filtered through a silica-free paper inserted in a rubber funnel. The acid was stored in rubber bottles. This acid was used in varying amounts without affecting the final titration, while varying amounts of C. P. market acid labeled “silica-free” gave consistently varying results. A silica determination on this so-called C. P. acid showed it to contain the equivalent of 0.32 per cent hydrofluosilicic. To make absolutely certain that silica in hydrofluoric acid raised results, 10 cc. of laboratory acid to which were added 2 cc. of 35 per cent hydrofluosilicic were used. The final titration was by far in excess of what it should have been. The following results are typical : HFa CC
.
5 10 10 10 15 20 10
+
Eouivalent NaOH
cc .
28.0 26.1 26.6 26.6 2.5 4 25 4 25 4 35 5
2 cc HZSiFa The first four results were obtained with market acid and the remainder with acid prepared in the laboratory. a
The sodium fluoride used in the foregoing experiments was prepared from the laboratory acid by adding half as much pure sodium carbonate as is necessary to neutralize the acid. The precipitated acid fluoride was filtered, dried, and gently ignited to drive off the acid. Heating was continued until 1 gram of the salt showed no acid reaction when dissolved in water. All the results given above are much too high except where the laboratory acid was used alone, in which the number of cubic centimeters (25.4) alkali is equivalent to 99.96 per cent sodium fluoride. It seems to be exceedingly diacult to obtain hydrofluoric acid free from silica. Possibly the only way to obtain it is to use the method herein described. But there is no need of this since an acid containing silica will raise the results by a certain amount pending the amount of acid used. If the error is ascertained a t the outset on, say, 10 cc. of the acid, it can be deducted from all runs as a blank. 2-It is a known fact at sodium acid fluoride is not very stable. To be sure, a t room temperature it is quite stable, but a t the temperature of the water bath its stability is doubtful. A number of samples were run on a moderately pure sodium fluoride. While still reeking with moisture and acid, they were removed from the water bath and allowed to dry a t room temperature. When the odor of hydrofluoric acid was no longer perceptible, they were titrated. Results were surprisingly uniform Other samples were run in the regular fashion, except, after dryness was reached, they were allowed to remain on the water bath for varying lengths of time. The results below are typical:
309
the higher were the results. These high results were attributed to the displacement of hydrofluoric acid by the sulfuric acid, since often the odor of acid were perceptible during boiling. A series of experiments omitting the boiling were then run. The results commenced to run consistently for the first time. A sample was run to which were added 0.05 gram of sodium carbonate and 0.05 gram of sodium silicofluoride. The original sample tested 0.26 per cent carbonate and 0.35 per cent silicofluoride. With the addition the theoretical values are 5.23 per cent carbonate and 5.31 silicofluoride. The analysis showed 5.20 per cent carbonate and 5.21 per cent silicofluoride. Several other runs were made in which the boiling was omitted, with equally as good results. &-Since prohibition has been in effect the chemist finds i t exceedingly difficult to obtain ethyl alcohol. Even alcohol denatured with 10 per cent methyl, which serves almost as well as ethyl alcohol, cannot be obtained without duly going through some “red tape.” In view of these deplorable facts, various easily obtainable alcohols were tried as substitutes. Methyl, isopropyl, and propyl alike proved to be poor substitutes. Finally, alcohol denatured with pyridine and benzene was tried and, even though the benzene did precipitate, it served surprisingly well. While not equally as good as ethyl alcohol, it will be satisfactory for most commercial analyses. 6-The insoluble residue must be determined as herein described if a total analysis that inspires confidence is desired. Most methods recommend dissolving in water and filtering, which is all right provided the fluoride is neutral or acid; but if it is alkaline the insoluble residue and sodium fluoride contents are increased a t the expense of sodium silicofluoride (Note 1). To ascertain the difference on a sample containing 6 per cent of carbonate and 6 per cent of silicofluoride, two samples were run for insoluble residue, one destroying the alkali before diluting, and the other by merely dissolving. The insoluble matter in the former case amounted to 0.13 per cent, while the latter amounted to 0.04 per cent.
A Substitute for Hard-Glass Ignition Tubes’ By George W. Muhleman HAMLINE UNIVBRSITY, ST. PAUL,MINX.
those experiments in general chemistry requiring the ItoSwaste use of hard-glass ignition tubes the beginner is liable a great deal of material and time in cutting and
fire-filing glass and in assembling apparatus. Indeed, in lecture demonstrations with the hard-glass ignition tube the experiment is often interrupted by the cracking of the tube. Time heated NaOH uivalent N a F To obviate these difficulties a metallic ignition tube has Sample Minutes cc. Eq Per cent 1 Room temperature 24.50 99.28 been devised. It consists of a bronze tube 20.3 cm. (8 inches) 2 15 24.45 99.08 long and 2.54 cm. (1 inch) in diameter. To each end is 98.67 3 30 24.35 97.45 4 45 24.05 fitted a screw cap into which is brazed a metallic tube 15.2 Excellent checks were obtained in the first two experiments; em. (6 inches) long and of approximately the same diameter checks were not quite so good in the third; and in the fourth they as ordinary glass tubing. Rubber connectors are used were exceedingly poor. The difference between the first and to attach this apparatus to gas generators. By using a second is not great enough to warrant the use of the more lengthy cap for one end of the tube one has a still that can be used first procedure. 3-Instead of using the more expensive platinum, a casserole, for the dry distillation of coal, wood, or any organic matter. the inside of which has been carefully paraffined, can be used An ordinary porcelain boat easily passes into these tubes, equally well. The best way to do this is to etch the inside of the and they do not leak gas. These tubes have been used casserole with 30 per cent hydrofluoric acid, and dry thoroughly in the laboratory for three years and are still serviceable. before coating with paraffin. The following experiments may be performed with this 4-The experience gained in the experimental work led to the belief that the alkalinity of sodium fluoride is probably not due apparatus : (1) reduction of copper oxide with hydrogen, entirely to sodium carbonate. This conclusion is based upon (2) reduction of iron oxide, (3) partial reduction of aluminium the manner in which the standard acid acts upon the dry fluoride. Samples received from various sources showed very little effer- oxide, (4) preparation of hydrogen by passing steam over vescence upon the addition of the standard acid and still an heated zinc, ( 5 ) preparation of water gas, (6) distillation of alkalinity of from 2 to 5 per cent of sodium carbonate was ob- different forms of organic matter.
tained, whereas a distinct effervescence was observed on samples, originally free from alkalinity, to which has been added from 2 to 5 per cent sodium carbonate. Throughout the analytical procedure sodium carbonate is mentioned, not because it is believed to be present, but because it is more convenient. Even though it might be partly the hydroxide, the error is small enough to be regarded as negligible. In the early stages of development, the standard acid was added, diluted, then boiled to remove carbon dioxide. High results were invariably obtained and the longer it was boiled
1
Received January 26, 1925.
$1800 Platinum Theft-The platinum ware which was stolen from the Department of Health Laboratory, Ohio State University, February 15, included 13 small dishes, 3 trays, 2 crucible lids, 3 perforated crucibles, and a small piece of scrap platinum. The robbery is similar to that a t the University of Akron, where 81200 worth of platinum was stolen, February 8.
,
