576 STATE BOARD OF AGRICULTURE. 



CONSTANCY OF THE NITROGEN-AMOUNT IN AIR CONFINED WITH LIVING 



INSECTS. 



Earlier in this paper, proof was promised for the statement that the 

 amount of free nitrogen is not appreciably diminished or increased 

 by insects during respiration. Much care was necessary in deciding the 

 question certainly, because of its importance in the method used for 

 estimating the percentage of oxygen (or other component gas) absorbed 

 from air confined with insects. Besides, Treviranus, 1831, was of the 

 opinion that insects excrete nitrogen in small amounts, very much as 

 they excrete carbon dioxide. The work of Sorg has already been men 

 tioned. Liebe,^ 1872, and Pott,- 1875, carried on experiments with cer 

 tain insects to determine the amount of carbon dioxide given otf per 

 unit of time and body- weight, but they did not determine the oxygen 

 used. Treviranus- is the only worker known to me who attempted to 

 estimate both the oxygen absorbed and the carbon dioxide given off 

 by insects in air. He published a table of his estimations, and explained 

 that oxygen was used in amounts greater than the carbon dioxide ex- 

 creted. Also, he says that in every case the volume of the air became 

 changed at fiirst; buit this, he though was only through the animal 

 swallowing a certain quantity of gas. He had observed gas taken into 

 the digestive canal of the leech and some other animals with suctorial 

 organs and seems to have concluded that it was the same with insects. 

 In four or five cases, he obtained a continued decrease in volume which 

 he thought really too great to be accounted for in that Avay. Still, he 

 drew his conclusions, from his other investigations, that the volume of 

 air with insects remained practically unchanged in respiration. To make 

 up the difference caused by the unequal exchange of oxygen and carbon 

 dioxide, he decided that nitrogen was excreted to the amount of that 

 difference. 



Other workers at that early time, using larger animals than insects, 

 fell into the same error, as later workers upon the respiration of mam- 

 mals have shown. 



It was only after a series of experiments that satisfactory proof was 

 finally obtained that the volume of nitrogen in air confined with in- 

 sects remains practically unchanged. 



First, specimens of Passalus cor nut us were confined in measured 

 amounts of pure hydrogen or of pure nitrogen (i. e,, free from oxygen) 

 for several hours at a time. In the case of both gases, after the carbon 

 dioxide excreted by the insects during the interval had been absorbed 

 the volume of the gas remaining was the same as at the beginning, 

 showing that no nitrogen had been added or taken aw^ay. Pure hydro- 

 gen was obtained by means of a Hempel hydrogen pipette and stored 

 in a gas container over potassium pyrogallate. The apparatus set up for 

 this purpose is shown in Fig. 5, (p. 30). Bulb "Z," of the pipette, contain- 

 ed in its lower part lumps of pure zinc supported by the end of a glass rod. 

 Bulb '^S" contained weak sulphuric acid. The container *'C" held 

 potassium pyrogallate, which was displaced into the aspirating bottle 



1. Liebe, Otto; Inaugural Address, Juiia, 1S72. 



2. Pott: Die Landwirthschaftlichen-Vesuch.s-Statioiien, etc.— Band XVIII, 1S75, p. SI. 



3. Treviranus, G. R.; Erschcinungen iiud Gesetzc des Organischeu Lpbens, lS'3l. \o[. 1, pj). 

 35S-361 — see also table at end of Vol. i. 



