532 



the manner in which the air enters and moves along to the centre 

 chamber (where the test-slip is hung at A), and figure 2 represents 

 a section of the lower half of the box where the air circulates in the 

 opposite direction, leaving the box on the side opposite to that on 

 which it had entered. 



The box has been tested and found to work well. 



On three different dates, when there was much ozone, test-slips were 

 hung in one box, whilst others were hung in another which had the 

 two entrances sealed up in order that no current of air should pass 

 through ; the result was satisfactory, viz. : 



Example. New ozone-box. New ozone-box sealed up. 



1 10 



290 



3 9i 



Then again, in five examples of test-slips being exposed without 

 any box, in comparison with those placed in this new box, the result 

 was : 



Example. In new ozone-box- Exposed to north without 



a box. 



1 10 9 



299 

 377 



4 10 5 

 520 



The ozone- box is capable of being suspended at an elevation above 

 the ground ; and this appears to be a great advantage, because eleva- 

 tion seems necessary in order to get a proper current of air to pass 

 across the test-slips ; indeed as an instance it may be mentioned, that 

 at an elevation of 20 feet there is almost always more indication of 

 ozone than at 5 feet. 



The plan adopted here is to suspend the box to a "]" support, it 

 being drawn up to its proper place by means of a thin rope passing 

 over a pulley ; and there is less trouble in examining and changing 

 the test-slips in this manner than there was in the old method. 



The box, as described, is made by Messrs. Negretti and Zambra 

 of Hatton Garden. 



It has been urged that a box was scarcely necessary for ozone 

 test-slips ; but as the papers fade on exposure to light, it must be 



