MARINE DEPOSITS OF PATAGONIA 183 



internal diameter and the rate of flow was adjusted until 253-4 rnillilitres were 

 delivered at tube in 12 min., this being the amount delivered at a rate of flow of 7 mm. 

 per second. The height of the water in the gauge tube g was then marked and the 

 apparatus was thus calibrated for the required rate of flow of water. Owing to the con- 

 striction caused by the screw clip e just beyond the junction of gauge tube g with the 

 down tube/, the water-level in the gauge tube varies, on the principle of the Venturi 

 water meter, with the velocity of the water flowing through the apparatus. If the 

 apparatus is to be used for rates of flow of very small amount the gauge tube g may 

 be placed at an oblique angle, instead of vertically, so that small changes in level cause 

 comparatively large movements of the meniscus along the gauge tube. 



In using the apparatus a weighed filter paper was placed in funnel m, the clips // and 

 k opened and the water turned on, the correct level in the gauge tube being verified. 

 The fine material in the vessel of water, separated from the coarser grades as described 

 above, was well stirred and poured into the levigator funnel / and the vessel well washed 

 down into it. The material and water is poured in gently on the side of the movable 

 septum s, away from tube o, so that swirling does not carry over coarse particles through 

 this tube. Separation begins immediately, the larger particles passing down the levi- 

 gator tube n and accumulating at the bottom of receptacle i, while the finer material 

 remains in the levigator funnel /, or is carried over into funnel m where it is caught on 

 the weighed filter paper. 



The amount of material placed in funnel / must be such that the filter m does not 

 become clogged and overflow before separation is complete. In practice this occurred 

 only on a few occasions with very muddy samples, when the levigation had to be 

 repeated with a smaller quantity of material. 



When separation is judged to be complete clips k and h are closed, when the material 

 in tube n settles to the bottom of receptacle i. Receptacle i is removed and its contents 

 turned out into a funnel containing a weighed filter paper, and well washed down. 

 Levigator funnel /, with its rubber junction and clip, is removed and emptied into 

 funnel m and well washed down. The filter papers and their contents from funnel m and 

 from the funnel containing the material from receptacle i are then washed, dried and 

 weighed. This gives the weights of the grades fine sand and silt, and these weights, 

 together with that of the material from which they were separated, which has also been 

 dried and weighed, give the total weight of the sample analysed. From this the per- 

 centages of the grades fine sand and silt and the percentage of all the other grades taken 

 together are found. The weights of the other grades, as found from the sieved sample, 

 when added together are therefore equal to the latter percentage of the total. From this 



. . , /percentage of grades together x weight of grade\ , _ / ,„ 4 .„„ /5 „r 



can be calculated v - 2 § s _^_ _ the percentage ol 



\ sum or grades / 



each grade in the complete sample. 



