546 



CHAPTER XXVII 



cult owing to the depth of foam or scum which forms on the surface. The 

 following method of determining the real level was shown the writer by Mr. 

 H. C. Sayre. To one end of a rod of wood a weight is fixed, such that the 

 rod will sink in molasses to a mark, the position of which on the rod is noted. 

 This rod suspended from a cord is let down into the storage tank until it 

 meets and floats in the molasses. The length of the string from the top of 

 the tank is observed, whence is obtained the level of the molasses below the top 

 of the tank. The foam, which may be a foot in depth, has a very small 

 influence on the depth to which the weighted rod sinks. 



Automatic Record of Density. — Langen's apparatus^ is shown in Fig. 35c. 

 The juice enters a containing vessel, /, overflows at d and passes away at h, 

 thus maintaining a constant level. Inside the narrow central part of the 

 vessel is a tube, e, to the lower end of which is attached a rubber baU, g. 

 This tube is filled with water, and the height to which the water rises is 



Fig. 



35c^ 



dependent on the pressure on the ball, which is in turn controlled by the 

 density of the material in the vessel /. The level of the water is recorded 

 through a float, c, carrying a pencil, a, bearing on the rotating cylinder, b. 

 The lower part of the tube, g, is formed into a spiral, so as to equalize the 

 temperature of the water therein and the juice in the vessel/. 



This apparatus, or others working on similar principles, are very useful 

 to obtain a record of the densitj' of the last mill juice and of the syrup, with 

 the object of checking the care exercised by the operatives. They do not 

 eliminate the necessity for taking regular samples, the results of the analysis 

 of which give the figures entered in the records. 



Sampling. — The control is vitiated by inaccurate sampling equall}' with 

 inaccurate analyses. The degree of exactitude demanded depends on the 

 purpose for which the sample is taken. General information only may be 

 required or the sampling may form part of a process on which a calculation 

 of recovery and losses is based. The second object requires as exact a sample 



