INDUSTRIAL A N D ENGINEERING CHEMISTRY
1278
of the titanous chloride solution can be avoided and the necessity for frequent standardization obviated if an airtight container is provided. The method is suitable for use in a commercial laboratory where control samples of potassium chlorate are regularly analyzed. If the standardization is performed by a capable person it should present fewer diEculties to the chemist inexperienced in chlorate analysis than the other. Reduction and Subsequent Determination by Standard Potassium Permanganate
In all methods under this head, the standardization of the 0.1 N potassium permanganate solution is the first consideration. It is advisable to standardize 0.1 N permanganate against sodium oxalate in the usual manner. The standardization may be checked, if desired, with 0.1 N sodium thiosulfate! previously standardized with resublimed iodine. The sodium oxalate used in the standardization must be obtained from the Bureau of Standards, as the purity of that obtained from manufacturing firms is not reliable. In the experience of this laboratory the use of sodium oxalate other than that from the Bureau of Standards has been shown to be the cause of discrepancies in results. Table I shows the variations. SODIUM OXALATE USED Bureau of Standards Chemically pure
Table I Weight used 0.1 N KMnOd Gram cc. Factor 0.-617 24.20 0.9973 0.1623 24.31 0.9965 Av. 0.9969 0.1828 24.23 1.0028 0.1627 24.23 1.0022 Av. 1.0026
Check using sodium thiosulfate: Cc. 0.1 N KMnOr Cc. 0.1 N thio 26.00 25.18
Thio factor 1.0290
KMnOI factor
0.9969
All the methods of th'is type depend upon the reduction of the chlorate by an excess of ferrous salt and the subsequent titration of this excess with potassium permanganate. The first method to be considered is that outlined in the United States Pharmacopeia: Transfer to a 250-1111. flask about 0.1 gram of potassium chlorate accurately weighed, and dissolve it in 10 ml. of distilled water, then add 25 ml. of acidulated ferrous sulfate (T. S.) to the solution. Insert a Bunsen valve in the flask and boil the mixture for 10 minutes. Cool the mixture, add 10 ml. of manganous sulfate (T. and titrate the excess of ferrous sulfate with 0.1 N potassium permanganate (V. S.). Run a blank on 25 ml. of acidulated ferrous sulfate (T.S.) and subtract the result of the latter titration from that of the former.
the excess ferrous ammonium sulfate is titrated with 0.1 N potassium permanganate. The difference between the two titrations is the number of cubic centimeters required to reduce the chlorate; 1 cc. 0.1 N potassium permanganate is equivalent to 0.0020427 gram potassium chlorate.
A sample of potassium chlorate was analyzed by this method with these results: 99.77, 99.67, 99.87, 99.75, 99.77 per cent-average 99.77 per cent. One drop in the,permanganate titration causes a difference of 0.00011 gram or 0.20 per cent in the result. To check the accuracy of this method two portions of this sample were weighed and made up to volume by two persons. These solutions were interchanged without knowledge of the weight the other recorded. Assuming the chlorate to be 99.77 per cent, each analyzed and calculated the number of grams present in the sample, with the following results: Gram calculated 0.5006 0.5002
( a ) Ferrous sulfate is less stable than ferrous ammonium sulfate. ( b ) It is more accurate to take more cubic centimeters of a less concentrated reducing solution when it has to be quantitatively measured, than 25 cc. of the concentration designated in the U. S. P. (c) It is better to titrate the sample and blank while hot, instead of after cooling, since the potassium permanganate is standardized against a solution a t 80' C.; also, in cooling, the vacuum produced in the flask may cause i t to collapse. Frankford Arsenal Method A weighed sample of 0.5 gram of potassium chlorate is dissolved in distilled water, diluted to 250 cc. in a graduated flask, and an aliquot portion of 25 cc. taken with a pipet which has been standardized against the flask. This portion is run into a 250-cc. Erlenmeyer flask, diluted with about 10 cc. water, and 10 cc. sulfuric acid (1:1) added. A Bunsen valve is inserted into the flask, the contents of which are heated nearly to boiling; 50 cc. of a 4 per cent solution of Mohr's salt (ferrous ammonium sulfate), which has been acidified with 1: 1sulfuric acid, are added, and the solution boiled for 2 minutes. The value of 50 cc. of Mohr's salt solution is determined by titrating against 0.1 N potassium permanganate solution. After boiling 2 minutes,
Gram weighed 0.5007 0,5002
Difference 0.0001 0.0000
The value of a quantitative method of analysis depends primarily upon its accuracy, but once accuracy has been established, the choice of the method to be used is governed by its ease of manipulation and economy of time. Judging by these facts, this last method reviewed proved most satisfactory in all respects. Summary
1-Three types of methods for the analysis of potassium chlorate have been reviewed. 2-Methods depending upon the reduction of the chlorate to chloride and subsequent determination of the chloride are unsatisfactory. 3-A method depending on the reduction by standard titanous chloride solution is accurate but impractical except for routine control analyses. 4-The method given in the U. S. P. is open to improvement. &The method used a t the Frankford Arsenal is both satisfactory and accurate.
New Technical Uses for the Filter Pump'
s.)
This method was found to be accurate, but it has the following disadvantages in comparison with the slightly different method used a t the Frankford Arsenal:
Vol. 17, No. 12
By E. A. Vuilleumier DICKINSON COLLEGE, CARLISLE, PA.
HE water that issues from the familiar filter pump is mixed with a large volume of air. This has suggested a number of useful purposes to which the aspirator might be applied outside of the chemical laboratory: 1-As is well known, air is of value in the purification of water, especially when the water is contaminated by sewage. The normal oxygen supply may be very materially increased with the help of an aspirator. 2-In applying sprays for insecticidal purposes by means of force p m p s , one of the chief difficulties is in attaining spreading power. The air that is mechanically carried along with the liquid passing through a filter pump may be of assistance in achieving the desired result. 3-In washing precipitates by decantation, where hand or mechanical stirring is impractical or inconvenient, the air will perform the agitation a t practically no additional cost. 4-When a shower bath head is attached to an aspirator, the water and air mixture is found t o exert a new, pleasant sensation upon striking the body. This might be of especial interest to hydrotherapists. &The taste of drinking water can be improved by attaching a filter pump to the faucet. 6-The amount of dissolved oxygen in aquariums can be increased in the same way. 1
Received October 12,1925.
