OF ARTS AND SCIENCES. 125 



titles of sulphide of antimony, we in the first j^lace employed the porous 

 filtering cones described by Prof. C. E. Munroe ; * but we found these 

 both too limited in capacity, and too susceptible to hygroscopic influ- 

 ences, to give the degree of accuracy we required. 

 We were therefore led to devise the following 

 apparatus, which Figures 1 and 2 will help us to 

 describe. The most essential part of this appa- 

 ratus is the platinum " rose " represented by Fig. 

 I. This is cemented bv sealinor-wax to the end of 

 a glass tube, and to its perforated base the small 

 filters are applied. The glass tube is so cemented Fig. 1. 



into the neck of the " rose " that the end may reach quite down to the 

 perforated plate, and thus draw up all the liquid which collects in the 

 hemispherical cup. Moreover, the perforated plate has an unbroken 

 rim about -jV ^^ ^^ '^^^^ wide around the edge, which is sufficient to 

 prevent any solid particles from creeping by the edges of the paper 

 disk. The success and rapidity of the filtering depend on the proper 

 construction of the perforated disk, and we obtained the best results 

 only after several trials. The holes should be smoothly perforated 

 about 5^0 of an inch in diameter, and as numerous as possible, leaving 

 the unbroken rim described above. After the perforations are made, 

 the face of the plate should be ground perfectly smooth. We use 

 two sizes of these " roses," in one of which the hemisphere is \^ of an 

 inch, and of the other li inches in diameter; but the smaller is the 

 more useful, and is sufficiently large for all ordinary purposes. A disk 

 of washed Swedish filtering paper, || of an inch in diameter, weighs 

 only about 20 milligrammes ; and, to give an idea of the rapidity of the 

 filtration, it is sufficient to say that, under a pressure of 50 centi- 

 metres of mercury, these filters will pass from 20 to 30 litres of clear 

 water in an hour. We have been greatly indebted to Messrs. John- 

 eon, Matthey, & Co., of Hatton Garden, London, for the care they have 

 taken in the construction of these " roses ; " and they can be procured 

 of them through the mail. The cost of the smaller size is fifteen 

 shillings sterling. The construction of the rest of the apparatus is 

 made clear by Fig. 2. One of the stems of a glass three-way tube is 

 clamped to an arm which can be raised or lowered on the vertical bar 

 of an elevating stand by a rack and pinion movement, which ought, 

 however, to be so loose, that the arm can be pushed suddenly up 

 when necessary. By its second stem, the three-way tube is connected 



* American Journal of Science, May, 1871. 



