RESE-IIRCHES O S XITROUS OXIDE BY ARTHUR NEVILLE COPNALL B E S S E T T
It-hilst the results obtained by the use of nitrous oxide gas in anaesthesia have generally been satisfactory, yet on occasion ill effects have been observed, the causes of which have not been understood. Consequently the chemical purity of the gas has been suspected, and it has been felt by anaesthetists that some definite tests should be available for detecting impurities which might be present. In 1911 Dr. Warren Smith, in conjunction with E. D. Lemanl investigated the problem for the purpose of submitting some non-official tests for insertion in the American Pharmacopoeia. More recently Dr. Hadfield? (Secretary of the Anaesthetics (‘oinmittee of the Medical Research Council) discussed the subject in a paper entitled “Sitrous Oxide: ita Impurities and the Establishment of Testa suitable for Official Adoption.” He pointed out that there are no official cheniical tests for nitrous oxide in the British Pharmacopoeia and suggested that the tests given in the American Pharmacopoeia are inadequate and not sufficiently sensitive. Dr. Hadfield described other tests which niight be more suitable, but which he considered required further examination. The work described in this paper has been conducted in order to select standard methods and if possible to find simple routine methods for the analysis of some of the probable impurities in nitrous oxide, and further to examine the behaviour of these impurities in cylinders of the commercial gas. Sitrous oxide is produced by the decomposition of ammonium nitrate by heat. Detailed methods of its nianufacture and methods of testing its purity are given by Baster3 and by Crowel14. The ammonium nitrate used should be 99.8% pure and free from organic matter. If below this standard it should be dissolved in water, freed from chlorides and sulphates and recrystallised. Whilst there are several impurities which niight possibly be detected in commercial nitrous oxide, there is only one-nit rogen-which is found in comparatively large quantities. This impurity which is always kept as low as possible has in the past been regarded as harmless;. Recently however, it has been considered that a large percentage of nitrogen may be serious in that it might produce asphyxia. Small quantities of oxygen are usually found present, and also moisture, but the content of the latter is always kept low on account of freezing up in the valve. Carbon dioxide is found in nitrous oxide produced by some companies only. Its presence is, however, thought to be advantageous. Although there appears to be no record of 1
.J. Am. Chem. Soc., 33, 1 1 1 6 (1911I . Proc. Roy. SOC.hfed., XIX,2, 1 7 (19261.
rlnaesthesia and Analgesia, 111, 4, ‘Anaesthesia and Analgesia, 111, 4,
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carbon monoxide having been detected in nitrous oxide, yet its presence, as with the case of cyanogen, has been considered becauseof the possible presence of carbon or its compounds which are sonietinies added to the original ammonium nitrate. On account of the somewhat slow absorption of nitric oxide in aqueous solvents and of its extremely poisonous nature, this impurity has greatly concerned the nitrous oxide manufacturers and anaesthetists. Although, however, the higher oxides of nitrogen have been detected in nitrous oxide, the gas normally appears to be remarkably free from these impurities. Ammonia has been detected in American nitrous oxide, and hydroxylamine has been suspected; but these appear to be fairly easily removed when suitable scrubbing towers are used. The halogens, although usually tested for, do not appear to have been detected. Oil, arsine, and combustible gases have all been considered but are rarely tested for. It has been found in this research that nitrogen is always present in considerable quantities in commercial nitrous oxide. The oxygen content always small was of the order 0.3-0.;7
