"Two species and two different concentrations were used. The concentrations were chosen on the basis of toxicological work knowledge up to the year 197 5. A further consideration was the general requirement that the concentrations should fall within the toxic range of the compounds tested, but taking into account the varying susceptibility of the different species.

Experimental apparatus, determination of test gas

The experimental apparatus (see Fig. 1) consisted of

1. compressed air supply.

2. air cleaning with

a) potassium dichromate-sulphuric acid,

b) sodium hydroxide,

c) glass wool,

d) calcium chloride;

3. air condition:

temperature 23.0 °C ± 0.5 °C (maximum range),
relative humidity 60% ± 3% (maximum range);

4. air current flowmeter ;

5. test gas supply;

6. air/ test gas mixing chamber;

7. exposure chamber (3 m3 ; length: 3 m, width : I m, height : I m);

8. sampler and thermometer:

a) at the air/gas mixture entry,

b) on the side wall of the exposure chamber,

c) at the air/gas mixture exit;

9. air/gas mixture exit.

The correct air/gas mixture was achieved by pilot tests and constant controls throughout the period of exposure were carried out gas

chromatographically. Immediate correction was made if the concentration differed 3% from the nominal values (5 ,000 or 10,000 ppm

by volume of air).

Technical data (double-channel apparatus):

detector: WLD;

carrier gas: helium;

flow velocity : 950 ml/h;

column: 5% OV 101 on gas chromium Q

80-100 mesh ;

operating temperature: 30 ·c.”

Male and Female Beagle Dogs