m. INORGANIC PLANT CONSTITUENTS, 



Combustion Method. Provisional. 

 [See page 21.] 



Burn the material in a current of oxygen, using the form of combustion tube 

 devised by Barlow. 



(1) APPARATUS. 



Draw out at one end a combustion tube of Jena glass (60 or 70 cm in length and 

 1.5 cm in diameter) and bend it down. At about 30 cm from the bend fuse onto the 

 combustion tube a side tube of the same kind of glass, having an internal diameter 

 of 6 to 7 mm. Such a joint is made without special difficulty by a skilled glass-worker. 

 The section of the main tube designated in fig. 1 as AD is from 30 to 40 cm, depend- 

 ing on the number of boats to be used and the amount of substance to be burnt. A 

 convenient length for DB is 30 cm. This allows a little play at the end of the fur- 

 nace, marked in the figure by the line HH. The lateral tube rises vertically about 

 3 or 4 cm so as to clear the furnace, and ij then bent approximately at right angles 

 so as to rest on the side rail of the furnace. Dress the tube in the following manner: 

 At G place a perforated disk of platinum foil provided with a loop of platinum wire 

 as a handle. Push into place by means of a long glass tube. A plug of asbestos may 



FIG. 1. Combustion tube. 



be substituted, but the platinum is cleaner and more convenient to handle in 1 1n- 

 subsequent operations. If asbestos is used, it must first bo ignited in sin -h a way 

 that it does not come in contact with the naked 1'unsen (lames. Next fill in the 

 column of absorbing material F, from 12 to 20 cm in length, depending on ihe amount 

 and nature of the substance to be burned. Kr the absorbing material use sodium car- 

 bonate, free from sulphates. To avoid an excessive amount of salts in the final solu- 

 tion, use clean sand or bits of porcelain which have been impregnated with sodium 

 carbonate and dried. In this manner an absorption column of IT) cm may be ob- 

 tained without using more than L' or :'> grams of the salt . 



Press on top of the quartz-soda column, a spiral <>f platinum wire. K, one end of 

 which is formed into a hook. It should lit the tube, so as to act as a light support foi 

 the column. The front of the spiral should be directly opposite the opening of the 

 side-tube D. Introduce the weighed material, leaving a space about 5 or 6 cm long, 

 between the front of the boats and the platinum spiral at E, and place the tube in 

 the cold furnace. Insert the cork A, with the T-tube KS. Place a "safety-beaker" 

 containing a little water at C, in order to furnish a test as to the completeness of the 

 absorption. Connect the side-tube D with an oxygen supply, and the tubes K and 



oj. Amer. Chem. Soc., 1904, 26:343. 

 236 



