Use of stainless steel absorption tubes for the semimicro carbon-hydrogen combustion

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.