CHEMICAL SCIENCE. 239 



ESTIMATION OF ORGANIC MATTER IN THE AIR. 



The following lecture was given before the Royal Institution, London 

 (March 2-3th, 18-39), by Robert Angus Smith. It furnishes more complete 

 details of a process devised by Mr. Smith, than was given in the Annual of 

 Scientific Discovery for 18-39, pp. 262, 263. 



After describing the opinions concerning matter in the air, and the attempts 

 made to estimate the amount, the lecturer described a method of obtaining 

 the relative quantity by means of mineral chameleon, permanganate of pot- 

 ash or soda. This mineral had been proposed by Forchammer, as a mode of 

 estimating the organic matter in water, but it was capable of estimating 

 quantities much more minute. At first, the air was passed through the so- 

 lution of chameleon, but this was not found to cause complete action. It 

 was necessary that the air should remain for some time in contact with the 

 solution to be decomposed. It was then ascertained that the relative amount 

 of organic and other oxidizable matter in air could be found by a simple 

 metrical experiment in a few minutes. In woi-king out this idea, it has been 

 found that a vessel of the capacity of 80 to 100 cubic inches is the most 

 convenient. This is equal to, or rather less than, a quart and a half. The solu- 

 tion used must be extremely weak; GOO grains of it are required to decom- 

 pose 5 grains of a standard solution of oxalic acid. The standard solution 

 of oxalic acid is so made that 1000 grains neutralize 1 grain of carbonate of 

 soda. A thousand grains contain therefore I 1 18-1 grains of crystallized oxalic 

 acid. To prepare the solution a manganate was formed by heating nitrate and 

 carbonate of soda and manganese, assisted by a little chlorate of potash. There 

 was the most minute trace of nitrate remaining in the solution. A solution 

 of this manganate was made in pure water, and carbonic acid passed through 

 until a i-eddish purple shade was obtained. It was then tested by oxalic acid, 

 adding three or four drops of pure sulphuric acid. Pure water was added, to 

 dilute it. The solution is apt to change, even when it is hermetically sealed 

 in a glass tube. It is found readily to change when exposed to air. The 

 strength is extremely small. A few grains of the ordinary solutions of 

 manganese used will make some thousand grains of the solution here em- 

 ployed. The reason of this lies in the extremely small amounts of organic 

 matter found in even the worst air. The vessel used is simply a bottle, with 

 a perforated stopper, through which pass two tubes. To one of these a stop- 

 cock is attached, to the other a clasp or stop-cock. The standard size pro- 

 posed is 100 cubic inches; and to this all the experiments have been reduced; 

 the vessels actually used contain between 80 and 100 cubic inches of air. 

 The stop-cock is of glass, or of hard caoutchouc, which is better. When the 

 bottle is to be filled with the air to be tested, the stopper is to be removed, 

 and the pipe of an exhausting pump is inserted, reaching to the bottom of 

 the bottle. The pump is made like a cylindrical bellows of about 8 inches 

 long Avhen stretched out, and 4 in diameter, and is compressible into the 

 thickness of about. 2 inches. The sides are made of thin Mackintosh cloth. 

 By the use of the pump the air of the vessel is removed, and the external air 

 of course enters. A few strokes of the pump are sufficient, i. e., from six to 

 ten. The test-liquid is poured into a graduated tube or burette, containing 

 somewhat more than will be required. A portion is then poured into the 

 tube which passes through the stopper, and the stop-cock is opened to allow 

 it to pass. Small quantities are used. When it has -entered the bottle, the 

 liquid is made to spread over the sides, and time given it to be exposed to 



