September15,1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
hot water, and the solution cooled t o room temperature. The solution is filtered on a 9-cm. paper containing some ashless paper pulp and the paper and residue are washed 18 or 20 times with 2 per cent ammonium nitrate solution to remove sodium salts. The paper and precipitate are ignited in a platinum crucible at a dull red heat until the carbon of the filter paper has been completely burned, fused with 1 or 2 grams of potassium pyrosulfate, and the titanium is determined colorimetrically. The weight of titanium found, multiplied by 3.16, gives the weight of TizPzOsto be deducted from the combined weight of zirconium and titanium phosphates. The weight of ZrPz07found, multiplied by 34.39 and divided by the weight of sample taken, gives the percentage of zirconium. Should the amount of titanium found account for the greater part of the combined weight of zirconium and titanium phosphates, then it is suggested that more 30 per cent hydrogen peroxide be added than that used for the colorimetric determination and the zirconium precipitated by the addition of 3 grams of diammonium phosphate, digestion, filtration, and ignition as described in the previously cited article.
It is well known that Zr(HPOJ2 is completely precipitated from relatively strong hydrochloric acid solution in which the iron is present in the ferrous condition. Hence, in dealing with plain carbon and manganese steels the treatment with hydrogen peroxide may be omitted. However, in working
335
alloy steels, especially those containing strong carbide-forming elements, the addition of hydrogen peroxide is necessary for the decomposition of the material. The results obtained by the procedure described are shown in Table I. TABLEI. DETERMINATION OF ZIRCONIUMIN STEEL STEEL ZIRCONIUM ZIRCONIUM TAKEN ADDED FOUND ERROR Grams Gram Grana Grana 1 Plain C 10 0.00047 0.00045 -0.00002 2 PlainC 10 0.00094 0.00093 --0.00001 3 Plain C 5 0.0045 0.00455 $-0.00005 4 CrWVa 5 0.00235 0.00284 --0.00001 5 CrWV 10b 0.00094 0.0009 --0.00004 0 Bureau of Standards standard sample 50 A. b Two 5-gram portions were taken and the precipitates combined after making the sodium carbonate fusion to separate the tungsten.
EXPERI- KINDOF MENT STEEL
LITERATURE CITED (1) Cunningham, T. R., and Price, Ed., 3, 105 (1931).
R. J., IND.ENQ. C~nnf.,Anal.
RECEIVED June 1, 1933.
Microburet for Potentiometric Microanalysis H. L. LOCHTEAND ANNA HOOVER, Department of Chemistry, University of Texas, Austin, Texas
R
ESULTS obtained by the junior author show that then assembled as shown and with the stopcock open and the micropotentiometric titrations using 1 cc. or less of buret filled with water the braking capillary is shortened by solutions with a normality of 0.1 to 0.01 are feasible and yield breaking off small pieces until drops are delivered st the rate an accuracy in favorable cases of 0.1 to 0.2 per cent, provided of 60 to 120 per minute. The next adjustment is that of the capacity of the tube the volume increments near the equivalence point are sufficiently small and uniform. The remarkable results just above the stopcock. If this is too large, a single turn of the reported by Schwarz (3) more than confirm the authors' stopcock results in delivery of several drops; if it is too conclusions in regard to the applicability of potentiometric small, a turn does not always yield a drop. The capacity titration methods to small volumes. Their early results is adjusted by changing the length of glass rod inserted above led to the development of a buret that delivers dependably the stopcock until single drops are obtained on turning the single uniform drops with a volume of about 0.01 cc. Since cock once. In use the pipet is filled by removing the braking capillary graphical or, preferably, Hahn's methods (1) permit estimaand filling by suction through a piece of rubber tion of the end point to one-tenth of this increment, tubing. In titrations the solution-may be added it is evident that the accuracy obtainable in suitable titrations is satisfactory for any ordinary micro rapidly until within 0.1 to 0.1.5 cc. of the end point. A few drops a t a time are now added until the uses. potential shows that the end point is approaching. Figure 1shows the buret finally adopted. For conThe exact volume used thus far is now read with venience in cleaning and in building and adjusting the the aid of a lens and further additions are made various parts, these were merely connected by highin single drops until 3 or 4 drops past the end point. grade clean rubber tubing a t the places shown. A Since several minutes are usually required1 to obtain ground-glass joint could be substituted for the uppera stable potential, the exact volume may be read most connection and the others could be eliminated again in the immediate neighborhood of the end point. by fusing the parts together, but this would involve The exact end point is then determined by one of the considerable cost and inconvenience and would yield methods mentioned and the volume read to 0.1 drop. no increase in accuracy. The graduated section is The drop volume should be redetermined daily by obtained from a high-grade pipet graduated to 0.01 counting the number of drops of the solution decc. and delivering 1 cc. The dimensions shown were livered between the 0.5- and 1.0-cc. marks. Since found satisfactory and, in case of the tip, essential. the drop volume depends partly on the hlydrostatic The tip with the length shown has a capillary with head, very accurate work requires determination, an outer diameter of about 0.5 mm. It is paraffined once for all, gravimetrically of the relation between by passing a continuous stream of low-pressure air drop volume and buret reading, but this precaution through it while dipping momentarily into melted is hardly necessary in ordinary work. The time reparaffin and then cooling till this solidifies. A tip quired for a complete titration with this buret is not that ceases to give small drops may often be repaired greater than that used with macroburets. by connecting to the air supply and remelting the paraffin by holding it above a flame. LITERATURE CITED The braking capillary a t the top is similar to that (1) H a h n , Z.anal. Chem., 87,263 (1931). of Ormond (2) but made from ordinary glass tubing (2) Ormond, Ibid., 75, 209 (1928). I6'MM. that is permitted to thicken in the flame and is then (3) Schwarz, K., Mikrochem., 13, 6 (1933). drawn out to a very fine capillary. The parts are FIGURE 1 RECEIVED May 23, 1933.
