November 1, 1894.] 



KNOWLEDGE 



259 



over a vast number of particles. The larger particles 

 have devoured the smaller, and inanimate cloud particles 

 have been struggling for " the survival of the fittest." 



Steam escaping into the air has been observed to be 

 coloured when seen against the sun. Sometimes in that 

 case the sun appears like silver (light blue), blue or green. 

 Mr. Lockyer saw the sun look vivid green through the 

 steam of a little paddle-boat on Lake Windermere. 

 Though the shadow of an ordinary steam jet on a white 

 screen is nearly colourless, yet when it is electrified the 

 shadow becomes of a dark orange-brown colour. 



In studying the subject, Mr. Aitken has enclosed the steam 

 jets in tubes. For a jet from a nozzle of one millimetre 

 bore, a tube of seven centimetres diameter and about fifty 

 centimetres long is employed. The steam nozzle should be 

 placed outside the tube and a little to one side, so that the 

 eye can be brought into a line with the axis of the cylinder. 

 This is a beautiful experiment. When the amount of 

 steam, dust, and other conditions are properly proportioned, 

 the colours seen through the tube are very attractive. 

 With ordinary condensation the colour varies from a fine 

 green to lovely blues of different depths. The pale blues 

 equal any sky blue, while the deeper blues are finer than 

 the dark blues seen in the sky, as they have none of the 

 cold hardness of the dark sky blues, but have a peculiar 

 softness and fulness of colours. 



Suppose, now, the tube is fitted up pointing to a clouded 

 sky, and that the steam jet, under slight pressure, is blow- 

 ing through it. If the exit end of the tube be open, very 

 little colour is visible ; but if the end of the tube be 

 partially closed with a glass plate to prevent a draught, 

 the tube looks as if filled with a transparent coloured gas. 

 The first decided colour is generally green, then blue of 

 different shades. 



If, now, the number of the dust particles in the tube be 

 increased, or the pressure of the steam be increased so as 

 to command some negligent dust particles to seize the 

 moisture and add to the number of cloud particles, thereby 

 making the steam more dense, then the colour seen through 

 the tube also changes. If the colour was green, it now 

 becomes deep blue ; and if the ordinary condensation gave 

 blue, the dense condensation (a strange but unavoidable 

 connection of words) produces a dark yellowish-browu. 

 But between the blue and the yellow there is always an 

 intermediate stage, when all colour disappears and the 

 light is simply very much darkened. Condensation of the 

 denser kind may be also produced by passing a flash of 

 electricity through the jet, by a supply of cold air, or by 

 placing an obstruction in fi-ont of the nozzle ; for there 

 are five ways of producing a denser form of condensation 

 of steam. 



From this it is seen that the colour produced by the 

 small drops of water depends on the size of the drops, and 

 the depth of colour on their number. The most probable 

 explanation of these colour phenomena is that they are 

 produced in the same way as the colours in plates, some- 

 what after the manner Newton thought the colour of the 

 sky was produced. The order of succession of the colours 

 in thin plates is the same as in these condensation 

 phenomena. As no white follows the first blue, it seema 

 probable that the first order of colours is not observed ; 

 that the two generally seen are the second and third. 



These colour phenomena placed in Mr. Aitken's hands 

 an easy and simple way of estimating, in a rough but 

 useful way, the number of dust particles in the air of our 

 rooms, and sanitary officers might with advantage employ 

 the convenient apparatus. And Mr. Aitken invented the 

 koniscope for the purpose. Kmiis is the tiretk for dust, 

 and shopfu means " I see "; so the instrument is for detecting 



the quantity of dust in air by sight — in fact, by the colour 

 observed in the fog produced in the air by artificial means. 

 The instrument consists of an air pump and a metal tube 

 with glass ends (about the size of the one above described in 

 the experiments). Near one end of ihe test-tube is a passage 

 by which it communicates with the air-pump, and near 

 the other end is attached a stopcock for admitting the air 

 to be tested. Wet blotting-paper is attached to the inside, 

 to make more uniform the field of colour. The instrument 

 is not nearly so accurate as the dust-counter, but it is 

 cheaper, more easily wrought, and more handy for quick 

 work. All the grades of blue, from what is scarcely visible 

 to deep black-blue, are attached alongside the tube on 

 pieces of coloured glass, and opposite these colours are the 

 numbers of dust particles in the cubic centimetre of the 

 similar air, as determined by the dust-counter. While 

 the number of particles was counted by means of the dust- 

 counter, the depth of blue given by the ko]iiscope was 

 noted, and the piece of glass of that exact depth of blue 

 attached. A metal tube was fitted up vertically in the 

 room in such a way that it could be raised to any desired 

 height into the impure air near the ceiling, so that supplies 

 of air of different degrees of impurity might be obtained. 

 To produce the impurity, the gas was lit and kept burning 

 during the experiments. The air was drawn down through 

 the pipe by means of the air-pump of the koniscope, and 

 it passed through the measuring apparatus of the dust- 

 counter on its way to the koniscope. It may be remarked 

 that by a stroke of the air-pump attached to the koniscope, 

 the air within the test-tube is rarefied and the dust particles 

 seize the moisture in the super-saturated air to form fog 

 particles ; through this fog the colour is observed, and the 

 shade of colour determines the number of dust particles 

 in the air. When by the dust-counter the number of 

 dust particles in a cubic centimetre of the air examined 

 amounted to 50,000, the koniscope indicated that colour 

 was just visible ; when 80,000 were counted, the depth of 

 colour was said to be "very pale blue" ; when 500,000, 

 "pale blue"; when 1,500,000, "fine blue"; when 

 2,500,000, "deep blue"; and when 4,000,000, "very 

 deep blue." 



When making a sanitary inspection, the pure air should 

 be examined first, and the colour corresponding to that 

 should be considered as the normal health colour. Any in- 

 crease from the depth would indicate that the air was being 

 gradually contaminated, and the amount of increase in 

 the depth of colour would indicate the aniotmt of increase 

 of pollution. Mr. Aitken thinks that the koniscope will 

 be serviceable for sanitary inspectors for investigating 

 questions of ventilation in rooms lighted with gas, and for 

 other purposes. 



As an illustration of what this instrument can detect, 

 he gives this experiment, to show how the pollution taking 

 place in rooms by open flames may be traced. The room 

 in which the tests were made was 24 by 17 by 13 feet. 

 The air was examined before the gas was lighted, and the 

 colour in the test-tube was very faint, indicating a clear at- 

 mosphere. In all parts of the room this was found the same. 

 A small tube was attached to the test-tube, open at the 

 other end, for taking air from different parts of the room. 

 Three jets of gas were then lit in the centre of the room, 

 and observations at once begun with the koniscope. 

 Within thirty-five seconds of striking the match to light 

 the gas the products of combustion had extended to the 

 end of the room ; this was indicated by the colour in the 

 koniscope suddenly becoming of a deep blue. In four 

 minutes the deep blue-producing air was got at a distance 

 of two feet from the ceiling. In ten minutes there was 

 strong evidence of the pollution all through the room. In 



