Library

Notes: Summary A Garner balance is described which by means of a vertical suspension fiber is said to be capable of weighing a 5-g load with a sensitivity better than that attainable with the ordinary knife-edge balance. Its weighing chambers were especially designed to accommodate light absorption tubes for the determination of carbon and hydrogen. A practical system for eliminating vibration and furnishing a suitable mounting for sensitive quartz fiber balances in the industrial laboratory is also reported. Under a 5-g load, the Garner balance was found to give strict proportionality within±0.001 mg between torsion and weight. It reproduces within ±0.26μg when weighing a 0.4-g platinum boat with the torsion fiber under continuous strain.

Notes: Summary The reproducibility of weighing the mass of small-size glass Ascartte and Drierite absorption tubes with 0.25-mm capillaries on the Garner balance has been investigated. A standard error of estimate for the Ascarite tube was found to be ±1.65μg and for the Drierite tube ±2.65μg. Corresponding figures for light-weight aluminum absorption tubes with 0.34-mm capillaries were considerably higher. Filled glass absorption tubes standing idle in the room were found to exhibit weight increases with respect to time of the order of 0.201μg/min. for Ascarite and 0.251μg/min, for indicating Drierite. Tubes with larger capillaries (0.34mm) showed a more rapid weight gain. Absorption tubes filled with oxygen undergo a loss in weight, which remains the predominating phenomenon during the first 2 hours. A limiting factor is indicated by failure to obtain consistent blanks.

Notes: Summary A rapid procedure for chlorine in milligram samples by a method combining thePregl microcombustion and theNorthrop potentiometric titration is described. Accuracy and precision are reported for 5 determinations on each of four test samples. Similar data are given for three water-soluble organic hydrochlorides where only the potentiometric titration part of the procedure is involved. A decimilligram procedure by the combinedPregl-Northrop techniques at the 0.3-mg level and theNorthrop titration for the decimilligram analysis of water-soluble organic hydrochlorides is described.

Notes: Summary A course in microchemical training suitable for students who will enter the profession of chemistry must be carefully planned not only on account of the increased volume of microchemical knowledge, but also because of the growth of science in general. — For those in America intending to enter the industrial field of microchemistry a background of general knowledge is just as important as specialized training in microchemical science. — A list of lecture topics in quantitative organic microanalysis as given at the City College of New York has been reported and the justification of certain topics on this list has been commented upon. — A choice of six determinations selected to give the student an optimum experimental technique in the short space of time available has also been given. — Industrial microanalysis in America requires in addition to a thorough training in the subject, an ability to master new procedures within a short time and a talent for making a critical evaluation of a given method in the literature before it is selected for trial. — Three typical industrial problems have been illustrated where a simple method in the literature has had to be considerably modified before it could serve an industrial purpose.

Notes: Summary The rapid procedure for the determination of sulfur in milligram samples by the silver absorbent method in the absence of halogen or alkali metal is described. Accuracy and precision are demonstrated by 10 determinations each, on four test substances. The reliability of the silver absorption was confirmed by determinations of sulfur in 26 other substances, the sulfur contents of which had been checked by either thePregl or theCarius method. A successful decimilligram procedure by the silver absorbent method is also reported, and its lower limit has been tentatively established at between 133μg and 53μg S in decimilligram samples. Results are given of a block experiment in which the effect of two variables, size of sample and type of equipment, was investigated. Statistical analysis of the data shows that the Garner quartz fiber balance when used with decimilligram apparatus is superior to a good microchemical balance with normal equipment in the range of 267μg to 133μg S.

Notes: Summary A temporary shortage of soft glass absorption tubes made it necessary to see if stainless steel ones could not be substituted in the carbon-hydrogen semimicro combustion. It was also of interest to find out if metal tubes would exhibit any greater constancy of weight on the microbalance. This latter point concerns the future possibility of carbon-hydrogen ultramicro analysis where absorption tube weighings will have to be more precise than today. Absorption tubes were made up from stainless steel into two types, semimicro and micro, and have been tested in routine analysis for performance. Both types had the same capillary dimensions as the regularPregl glass tubes, but differed in the length and diameter of the barrel. The semimicro steel tubes had about the same volume as the glass ones, but were much heavier, weighing about 16 g when empty and 21 g when filled. The micro metal tubes were a little heavier than the glass ones and weighed about 8.0 g when empty, as compared with 6.5 g for the glass tubes. They were of lesser capacity, however, being smaller in diameter and having a shorter length of barrel, so that when filled their total weight came to only 9.0 g which is about the same as that for glass tubes. A series of 14 determinations was made on each of three test substances using metal tubes and on each of two of the same samples using soft glass tubes. A statistical analysis of the variance appearing in each series of runs shows no significance at the 5% level in the carbon precision as obtained among the three compounds. There was also no significant difference at the 5% level in the precision obtained with either stainless steel or soft glass absorption tubes when either carbon or hydrogen was being determined; the criterion of such judgment being a comparison of the variance of 29 combustions using steel tubes with that of 28 combustions using glass tubes. This suggests that moisture on the glass or static electricity from wiping ordinarily have little to do with the precision of analysis as far as thesemimicro combustion is concerned. A series of 14 semimicro combustion analyses was also made on one of three test samples using the micro size absorption tubes. A comparison of the variance obtained here with that previously determined in the semimicro determinations on the same sample using large size steel tubes showed no significance at the 5% level between the carbon precision obtained with the micro and semimicro metal tubes. There was also no significance between the use of the micro metal tubes and the glass ones of larger volume. Stainless steel absorption tubes are as good as those made of glass for semimicro carbon-hydrogen analysis. They can probably function equally as well in the micro carbon-hydrogen procedure and perhaps even in an ultramicro method if their dimensions can be still further reduced.