654 REPORT — 1887. 



to be a usual property of bacteria ; many, liowever, reduce only to nitrites, while 

 others reduce to nitrogen gas. One of the latter class of bacteria produces much 

 nitrous oxide if asparagine be present in the solution. 



My own resultswere obtained in the present summer, and are as j-et incomplete. 

 About twenty organisms have been examined, most of which have been kindly 

 supplied in pure cultures by Dr. E. Klein, F.R.S. Out of these twenty about 

 thirteen readily reduce nitrates to nitrites, even at 20°; two organisms only reduce 

 in very nourishing liquids or at high temperatures ; five organisms do not re- 

 duce nitrates, even when air is nearly excluded. A considerable number, if not all, 

 of the reducing organisms produce nitrites, but no gas. 



It appears thus that the property of reduction, and the extent to which reduction 

 is carried, depends largely on the specific nature of the organism. When the chemical 

 properties of individual species of bacteria have been further studied, we shall be 

 able to classify them according to their behaviour, and be much aided in the 

 discrimination and identihcation of species. 



8. A neiv Metliocl for Determining Micro-orgnnisms in Air. Bij Professor 

 Carnellev and Thos. Wilson. 



This is a modification of Hesse's well-known process. It consists essentially in 

 the substitution of a tJat-bottouied conical flask for a Hesse's tube. Its chief 

 advantages are: — (1) Much smaller cost of flask and fittings as compared with 

 Hesse's tubes ; (2) very much fewer breakages during sterilisation ; (3) great 

 economy in jelly ; (4) freedom from leakage during sterilisation ; (o) results 

 not vitiated by aerial currents. 



TUESDA r, SEPTEMBER 6. 



The following Ileport and Papers were read : — 



1. Ileport of the Committee fir farther investi gating the Action of the 

 Silent Discharge of Electricity on Oxygen and other Gases. — See Re- 

 ports, p. 42. 



2. The Absorption Spectra of Hare Earths. 

 By G. H. Bailey, B.Sc., Ph.D. 



This paper is an examination of the conditions of observation of absorption 

 spectra with special reference to the recent announcement of the twenty new 

 elements of Kriiss and Nilson. The autlior finds that the strengths of the 

 absorption bands do not diminish equally in all parts of the spectrum when 

 the liquid is diluted. 



The presence of nitric acid also effects not only a displacement of the bands, 

 but also an alteration in their relative intensity. It is further pointed out that a 

 record of the strength of the bands in mixtures containing, in some cases, large 

 quantities of samarium and erbium, and in olhers none, cannot be used as a 

 means of comparison and deductions drawn from variations of intensity. Whilst 

 acknowledging that with due allowance for such factors some assistance may be 

 gained towards the course of fractionation, the author considers the announcement 

 of new elements quite premature, and only calculated to throw further confusion 

 into this already difficult field of work. 



3. The Absorption Spectra of the Haloid Salts of Didymium. 

 By G. H. Bailey, D.Sc, Ph.D. 



Bunsen has described certain variations that occur in the absorption spectra 

 given by crystals of the didymium salts. In this paper are detailed the variations 

 produced in the absorption spectra of crystals of didymium salts when examined 



