494 



CHAPTER XXV 



process gives the weight of an equal volume of the material being examined, 

 when the specific purity follows by a simple division, the degree Brix being 

 obtained from reference to tables. 



In very exact work all determinations should be made at one fixed 

 temperature, now selected as 20 C. As this is inconvenient in rapid 

 technical work in the tropics, the writer worked as follows : The mean 

 temperature of a laboratory was 27-5 C. The weight 

 of water in the pycnometer was determined for each 

 tenth degree between 25 C and 30 C. The weight of the 

 juice or other material was determined at whatever tempera- 

 ture obtained at the time of the determination, and was 

 compared with the weight of water at that temperature. 

 The corresponding degree Brix was then taken from a 

 table calculated for 27-5 0/27-5 C. The error intro- 

 duced by accepting an equal expansion for water and 

 sugar solutions between these limits does not appear till 

 the third decimal place in the degree Brix. 



2. A weight is suspended by a thread of silk from 

 the end of an arm of the balance. Its weight is observed 

 in air, in water and in the material under examination. 

 If x, y, z be the weights respectively in air, water and 



\ 



FIG. 327 



FIG. 328 



material, the specific gravity of the last is given by the ratio . This 



method may be employed on any balance as in Fig. 326, or the specially 

 designed Mohr-Westphal balance, Fig. 327, whereby the specific gravity is 

 read directly from the rider weights used, may be employed. 



3. The hydrometer, Fig. 328, consists of a glass tube on which is blown 

 an elongated bulb. Beneath this bulb is a second loaded with lead shot or 

 quicksilver. The upper portion consists of a slender stem, in which is located 

 the scale. When immersed in a liquid, the instrument will sink, or float with 



