CARBON IN ORGANIC SUBSTANCES BY THE KJELDAHL METHOD. 747 



shows the modification as used by the author. The ordinary tube requires to be 

 filled by means of a pipette, and the author found that, with the utmost care, there 

 was a slight risk of error, especially when working with strong solutions of baryta in the 

 laboratory, where the amount of carbonic acid is always greater than in outside air. 

 The possible error is not great, but if small quantities of organic substances are being 

 analysed, say 5 or 10 milligrams, the error is multiplied many times. In the subsequent 

 application of the method to water analysis even such a slight error would be serious. 

 The modification of the tube was devised for me by Mr Maitland Gibson, B.Sc, and in 

 every respect answers the purpose. It acts as its own pipette, containing 100 c.c. when 

 filled up to the mark near the bulb. The following is the method of filling. The 

 carefully washed and drained tube is rinsed out with the baryta solution to be used. 

 The end near the bulb is connected with the syphon tube from the store baryta solu- 

 tion bottle by the usual clip and rubber connection, and the other end is connected with 

 a water-pump. When the pump is turned on, and the clip released, sufficient baryta 

 solution is sucked into the tube, which is then disconnected from the pump and storage 

 bottle. Any excess is allowed to flow out till the level of the fluid is at the mark. The 

 connections between (D 5 ) and (Ej), between (Ej) and (E 2 ), and (E 2 ) and the pump are made 

 with tight rubber tubing vaselined inside. The other connections are rubber wired. In 

 conducting an analysis the weighed quantity of the substance in a platinum boat is 

 gently slid into the flask, taking care to avoid sparking of the substance on the inside 

 wall. The pump is put in connection with (D 5 ), and the rubber connected with the outlet 

 tube clipped at (a) and air aspirated through the flask and the rest of the system for 

 half-an-hour. This is to replace all the air in the apparatus by air free from carbonic 

 acid, &c. The rubber at (D 5 ) is now clipped, the pump disconnected, and the tubes filled 

 with baryta solution connected up. The cork of the flask is now removed and 10 or 20 

 c.c. of pure strong sulphuric acid put into the flask, taking care to prevent any acid 

 touching the neck of the flask where the cork is to be placed. The cork is quickly 

 replaced, (6) is clipped and (a) is opened, the pump now slightly turned on and the clip 

 at (D 5 ) opened. When bells of air are freely passing through the tubes a low flame is 

 applied to the flask. The heating is continued till the sulphuric acid becomes of a pale 

 straw colour. The current of air during the heating does not pass into the flask, but is 

 sufficient to determine a slow current of the gaseous contents of the flask in the direction 

 of the absorption tubes at (D) and (E). After the flame has been removed and cooling 

 begun, there is apt to be a very rapid suction of air into the flask, and hence, to avoid any 

 risk of the baryta solution being sucked back, the pump should be turned on a little 

 more for a few minutes. When the contents of the flask have cooled, 3 or 4 c.c.'s of a 

 boiled and cooled saturated and acidified solution of permanganate of potassium is added 

 by the bulb (B). It is added by means of a pipette with a fine limb, the clip at (B) is 

 relieved and the limb of the pipette inserted so as to be tightly grasped by the rubber. 

 This prevents any ingress or egress of air during the operation. The pipette is with- 

 drawn and the clip replaced. A low flame is now applied and the acid heated for about 



