Oct., 1946
COMMUNICATIONS TO THE EDITOR
2119
marine eggs13’rhas a number of theoretical connotations in the chemistry of proteins and their biological manifestations.
the accuracy is highest when the amount of isotopically labeled element added approximately equals the element content of the sample. The precision of oxygen determinations can be in(13) Tyler and Fox, B i d . Bull., 79, 153 (1940). creased simply by production of 0l8in high conCHEMISTRY LABORATORY IOWA STATECOLLEGE SIDNEY W. Fox centration. With about 20 at. per cent. 0ls an AMES,IOWA MARYJANE WARD average precision of *O.lyc of the oxygen content RECEIVED AUGUST19, 1946 of the sample analyzed should be attainable. The two experiments with formic acid show that i t is not necessary to completely combust the ELEMENTARY ISOTOPIC ANALYSIS. DETERMINsample to COZ and H20. As in Experiment 1, ATION OF OXYGEN equilibrium is attained, with CO and CHI in the Sir : At present oxygen in organic compounds is gas mixture. The most reliable Ol8 figures are obtained from usually determined by difference, that is, after deducting thie percentage of carbon, hydrogen the COz-peaks. The same method may be used and any other constituents from 100. The ter for solid organic compounds, and of course can be Meulen catalytic method, proposed in recent extended to inorganic compounds which would years, is the only direct method, but i t is compli- equilibrate with an 018-containing molecule. Description of our equipment and our detailed cated and requires careful manipulation. In view of the availability of mass spectro- results will be published elsewhere. The method graphs and heavy oxygen, i t occurred to us t o de- is now being extended to thg determination of velop an isotopic method. It is a very simple carbon, hydrogen and nitrogen. We are greatly indebted to Dr. Harry Thodlof adaptation of the isotope dilution principle originally introduced by G. v. Hevesy and F. Paneth. Toronto, Canada, for a generous supply of HzOl8, A known weight (a) of the substance to be ana- without which this investigation would not have lyzed (x% 0 ) is equilibrated with a known volume been possible. of oxygen gas (= b g.1, containing a known A. V. GROSSE LABORATORIES S. G. HINDIN amount of 0 ‘* (= m%) in e x c e s of the normal THEHOUDRY PA. A . D. KIRSHENBAUM concentration. The excess of 0l8in the mixture LINWOOD. RECEIVED AUGUST30,1946 after equilibration (= n) is determined by mass spectrograph. Thus a, b, m and n being determinable, it fclllows simply from the mixture rule BUBBLE FORMATION FROM CONTACT OF that SURFACES
Sir:
The equilibration takes place in a platinum testtube of 80 ml. volume, a t 600-800°, connected to a vacuum system. The time required is about onehalf hour. The following oxygen determinations show results obtainable by this method:
If commercial bottled soda water is poured carefully into a specially cleaned wet glass container the liquid remains free of bubbles and supersaturated with carbon dioxide, in contrast with soda water in an ordinary tumbler, where gas phases (gas nuclei) are present t o start bubble formation,
Detn. no.
1
4
5
Substance analyzed
2 Formic acid HCOOH (deficiency of 0 2 )
3
Formic acid HCOOH (excess of 02)
Acetic acid CHaCOOH
1-Nitroethane CHCHzNOz
Ethyl ether (CzHa)nO
38.2 20.0 (14.0)
60.4 22.2 (15.5)
26.0 36.5 (25.5)
20.9 31.4 (22.0)
52.70 12.03 (9.4)
2.00 0.85 70.8 69.5
2.00 0.69 60.8 69.5
2.07 1.50 53.4 53.3
2.10 1.64 40.3 42.6
2.145 1.15 19.8 21.6
a, i. e., mg. sample b , mg. oxygen-18 gas taken (using a t . wt. of 0 = 16.00) ( n l . a t N. T. P.) m, mole ‘j, 0’8.014 in b above normal concn. ( - 0.40%) n, mole % O1*.O’eof equilibrated mixt, (-0.40%) x , yooxygen in substance, calcd. from formula (1) % oxygen, theoretical.
These experiments, particularly 2 and 3, show even better .agreement than is to be expected. With the comparatively small 0ls concentration available to us, the average probable error is =t3.OojO of thle oxygen content. Since (nz - n) and n enter intb our equation, (1) For a comprehensive and critical review of this and other less developed methods see: P. J. Elvin‘g and W. B. Ligett, Chew. Rev., 84, 129-156 (19444,
A clean wet quartz rod in the soda water will also form no bubbles. However, if the quartz rod is drawn over the surface of the glass so as to produce a scratch, bubbles arise a t the contact of the two surfaces and a chain of bubbles may continue to form a t points along the scratch for a considerable time period. The above observations are widely known. We have, however, n o v been able t o show that bubbles
