330 H. A. Baker — Zoo.se Arenaceous Sediments. 



made glass stoppers, which are ground so as to fit well, and always 

 to enter the tube to the same depth. The stopper carries two short 

 tubes, to one of which is attached the jet-tube and to the other the 

 manometer-tube, carrying a graduated scale, intended for use with 

 a particular jet. By having corresponding pairs of jets and 

 graduated manometer-tubes, the same elutriator-tube may be used 

 repeatedly in carrying out different parts of the mechanical analysis. 

 In setting up the apparatus for the first time a jet and ungraduated 

 manometer-tube are attached, and the water turned on. The flow 

 is controlled by means of the screw-clip on the fairly thick-walled 

 rubber connexion attached to the lower end of the elutriator-tube. 

 With the water standing at some arbitrary point low down in the 

 manometer-tube, the outflow, in cubic centimetres per minute 

 from the jet, is determined by means of graduated measure and 

 chronometer. This point is marked and the current then increased, 

 so that the water stands at a higher point in the manometer-tube, 

 when a fresh determination of the outflow per minute is made. 

 Proceeding in this way a series of readings is obtained, which when 

 plotted on a graph are found to lie on a smooth curve, by means of 

 which the manometer scale can be constructed. This scale, therefore, 

 indicates from the height of the water in the manometer-tube, the 

 volume in cubic centimetres per minute flowing through the elutriator 

 when the appropriate jet is being used. 



A graph is constructed, showing for each elutriator-tube in use the 

 relation between the rate of outflow from the jet, in cubic centimetres 

 per minute, and the mean rate of the upward current in the tube 

 in millimetres per second. The graphs for all the tubes can be con- 

 veniently represented on the same diagram — they are, of course, 

 straight lines. 



In proceeding to make a separation of a sample at some specified 

 limit of diameter, the first step is to take the temperature of the 

 water which is to be used. Knowing this, the appropriate rate of 

 current is next ascertained. Then, on consulting the graph for the 

 elutriator-tube which it is proposed to use, the rate of outflow from 

 the jet required to give this current is readily obtained. It then only 

 remains to select a suitable jet and corresponding graduated 

 manometer-tube for attachment to the apparatus. 



The separation of a sediment into a large number of grades is a 

 tedious business, and much valuable time is often lost in removing 

 from the elutriator, drying, and weighing the successive remainders 

 as grade after grade is washed off the sample. In order to facilitate 

 the progress of the analysis the writer has devised the following 

 method of procedure which obviates the necessity of removing and 

 drying the material at the completion of each stage of the process. 

 It is necessary to know at the outset the weight of the empty 

 elutriator-tube together with its rubber connexion and screw-clip 

 at the bottom, but without the stopper and its adjuncts. A weighing 

 is taken before the elutriation is commenced, of tube and contents, 



