232 DE. A. MATTHIE8SEN ON THE EXPANSION 



I. On the Determination of the Coefficient of Linear Expansion by Heat of certain Glass 



Rods. 



I am indebted to Mr. F. Osler for kindly interesting himself in the subject, and 

 having had made at his manufactory two glass rods especially for these experiments. 

 From the ends of these rods pieces were cut, ground, and polished, to be used for weigh- 

 ing in water at different temperatures. The approximate mixture from which the rods 

 were made was 3 parts sand, 2 lead, and 1 alkali. 



The disposition of the apparatus used for the determination of the increment in 

 length may be seen from fig. 1 (Plate XX.), which needs some explanation. 



In the long zinc trough A (fig. 1) the rod was placed, the ends of it first passing 

 through holes in the ends of the trough ; into these openings were soldered pieces of 

 zinc tubing (fig. 2, a, a) of about 50 millimetres long, so as to serve both as a rest for 

 the rod passing through them, and as a means of making the trough water-tight. As 

 the greater part of the zinc tubing projected inwards, it was easy to draw a piece of vul- 

 canized rubber tubing over its end, and on passing the rod through this the trough 

 became water-tight. The few millimetres of the zinc tube projecting outwards served 

 to keep the ends of the glass rod (about 5-10 millims.), if not quite at the same tem- 

 perature of the bath, at all events very near it. Three other rests were placed in the 

 trough to support the rod (fig. 2, 5, h, b). The length, width, and height of the trough 

 were 1800, 180, 150 millimetres (measured inside). The long sides and top were made 

 double. Through an opening in the cover the thermometer T is fixed, the bulb reach- 

 ing in the water the level of the rod ; a smaller one (T,) is placed near the larger one, 

 so as to give the mean temperature of the column of the mercury not immersed in the 

 water ; that is, its bulb is placed near the middle of the exposed column. 



To give the necessary firmness to the apparatus, and to cause the expansion of the 

 glass to be indicated in only one direction, the following arrangement was made. A 

 hole was made in the wall so as to take the end e of tube B (fig. 1). Fig. 3 shows 

 the construction of this part of the apparatus. It consists of a stout glass tube fitted 

 into zinc caps, the ends of the tube touching the ends of the cap, so that when water 

 enters at d, it is forced to flow to the end of the zinc cap to enter the tube, and to make 

 its exit in the same manner at the other end. The zinc is connected with the glass by 

 rubber tubing ; the tube B, the end of which is cemented in the wall and supported by 

 two bricks, to which the tube is also cemented, thereby forming a solid resistance for 

 the one end of the rod to rest against. The communication between the other end of 

 the rod and the measuring-apparatus is similarly constructed (fig. 4) ; the length of the 

 fixed glass tube B being 300, and of the moveable one 350 millimetres. To steady the 

 latter as much as possible, the tube passed through a larger one cemented to the brick, 

 as shown in fig. 4. This allows the tube to move backward and forward with ease with- 

 out altering otherwise its position. It was kept pressing on the end of the rod by the 

 spring i (ordinary bell spring), a weight (h) hanging below it to serve to counteract the 



