CARBON IN ORGANIC SUBSTANCES BY THE KJELDAHL METHOD. 751 



Estimation of Carbon in the Analysis of Potable Water. 



Tiemann and Gartner * give a full account of the method of Wolff, Degener, 

 and Herzfeld for " estimating the carbon in the non-volatile organic substances contained 

 in drinking waters." 



Half a litre of the water is distilled until the residue in the retort is about 300 c.c. 

 In the distillate the volatile organic matter is estimated in terms of the amount of 

 permanganate of potassium used up in its oxidation. The residue in the retort is 

 evaporated down in a platinum dish to about 15 c.c. and then emptied into a flask of 

 about 300 c.c. capacity. The retort and platinum dish are rinsed out with about 10 c.c. 

 diluted sulphuric acid, and this is added to the contents of the flask and the whole 

 gently warmed to get rid of any carbonic acid from carbonates present in the water. 

 After cooling, 10 grammes of powdered bichromate of potassium are added, and the flask 

 (A) connected up with the apparatus as shown in Fig. 4. The flask is closed by a 

 rubber cork through which pass a thermometer, a funnel tube (b), and an exit tube 

 connected with a condenser (B), which is in turn connected with two U-tubes (C) and (E), 

 containing calcium chloride, and a third tube (D), containing ground metallic antimony. 

 F is a caustic potash bulb for absorbing the carbonic acid evolved in the operation. 

 The tube (d) is to prevent any chance of a reflux of carbonic acid or moisture, and is 

 continued by means of rubber tubing to a water-pump. To conduct the experiment 50 

 c.c. of diluted sulphuric acid (three parts acid and two parts water) are added to the flask 

 by means of the funnel tube (6), the stopcock of which is then closed. A low flame 

 is now applied to the flask, and after heating for about an hour it is boiled for about 

 ten minutes, and the pump turned on and the stopcock of the funnel tube opened. 

 Carbonic acid free air is sucked through the apparatus for twenty minutes in order to 

 sweep out the carbonic acid produced in the combustion. The metallic antimony in 

 tube (D) is for the purpose of absorbing any chlorine produced from chlorides in the 

 water. The potash bulb is disconnected and weighed ; the increase in weight represents 

 the carbonic acid produced in the operation. This method is in use on the Continent 

 for the analysis of potable waters. WiNOGRADSKY,t in a research on Nitrification, used 

 it for determining the carbon in organic matter ; but for determining nitrogen he used 

 the ordinary Kjeldahl method. In common with other observers, he has found the 

 method to give too low results. 



* Die Chemische und Microscopische Untersuchung des Wassers, 1889, p. 247, &c. 

 t Annates de Hnstitut Pasteur, Tom. 4, 1890, p. 257, &c. 



VOL. XXXVII. PART IV. (NO. 33). 5 Y 



