COLLODIUM SACS. 



499 



a test-tube and this is slipped inside of the sac. The first opening- 

 should be made in the bottom of the test-tube. A small narrow flame 

 is directed against the bottom, and, when the glass has softened, iTls 

 touched with a piece of drawn-out glass-tubing which is .then with- 

 drawn. The glass adheres and is drawn out into a thin capillary. This 

 is then broken off at about 0.5 cm. from the test-tube by a gentle tap with 

 the glass-tube. The flame of the blast-lamp is then directed against 

 the opening thus made. The broken edges sink to the level of the 

 tube and a round opening results. In this way a large number of holes 

 can be blown into the lower end 

 of the tube which is then con- 

 stricted in the manner already 

 described. The finished perfor- 

 ated tube has the appearance 

 shown in Fig. 71 e. 



The next step is to attach 

 the collodium sac to either of 

 these constricted tubes. The 

 open end of the sac is trimmed 

 square with scissors. The sac is 

 then placed between filter-paper 

 and dried ~by the application of 

 gentle pressure. It is especially 

 desirable to have the inside of 

 the neck of the sac perfectly dry. 

 The constricted tube is then in- 

 serted into the sac up to where 

 the constriction begins. This tube 

 and sac are now, carefully and 

 cautiously, rotated in a horizontal 

 position over a very small narrow flame. The modified Bunsen burner 

 provided with a pilot light is especially useful for this purpose. The 

 tube and sac are "held at a distance of 3-5 cm. above the narrow flame. 

 The collodium contracts down upon the glass and forms a perfect con- 

 nection. To make this absolutely tight the collodium, over the glass, 

 should be rubbed with a heated rod. In the absence of the burner 

 mentioned, a hot glass rod passed repeatedly over the end of the sac 

 will cause this to adhere to the glass. 



A silk thread is then wrapped over this portion of the sac; and, 

 finally it is thoroughly coated with collodium and allowed to dry. 

 The object of the silk thread is to enable one, later on, to firmly hold 

 the sac in a pair of forceps. The sac is now filled with distilled water 

 and the upper end of the tube is closed with cotton. The tubes thus 



FIG. 71. The preparation of collodium sacs. 

 a Test-tube, constricted and cut; b The sac 

 attached to preceding and filled with water; 

 c Same in test-tube on foot, in water, and 

 sterilized; e Test-tube, constricted and per- 

 forated; d The same covered with sac. 



