THE ALUMNI JOURNAL. 



i6i 



sampling in use in the assay laborator5^ 

 samples must be obtained that are repre- 

 sentative. Enlargements by photomi- 

 crography, and subsequent cutting out 

 and comparing by weight the tissues 

 printed and the remaining part may be of 

 service. Finally, much time must be yet 

 devoted in ascertaining the real and 

 permanent value of quantitative micros- 

 copical results to that of chemical results. 

 It is hoped that many will pursue similar 

 lines of research . — School of Mines, Cohctn- 

 bia College. 



Applications of the Ceritrfugal. With the in- 

 troduction of the various improvements in 

 -manipulations the variety of applications have 

 increased to such an extent as to render the 

 centrifugal an almost indispensible equipment 

 of the laboratory of the chemist. One of the 

 forms adapted for laboratory use is illustrated in 

 the Proceedings of the American Pharmaceutical 

 Association, 1893, p. 374, or Coblentz's Hand- 

 hook of Pharmacy, p. 214. 



Among the v^ious applications of this piece 

 of apparatus are the following : 



First. — For the microscopical examination of 

 starches, meal, etc., from 5 to 10 Gra. are taken, 

 well mixed with a little cold water, then 500 

 Cc. of water are added and then heated for fif- 

 teen minutes on a water bath until a smooth 

 paste results. Then 100 Cc. of this paste is 

 mixed with i Cc. of a 50 per cent, solution of 

 potassium hydrate, another portion of 100 Cc. 

 is mixed with 2 Cc. of sulphuric acid ; each of 

 these solutions is heated for thirty minutes on 

 the water bath. The fluids are then centrifuged 

 which causes the particles of the hulls to 

 separate in the bottom of the cylinders. The 

 -precipitates can be readily removed from the 

 almost clear supernatant fluid and examined 

 under the microscope. 



Second.— For the detection of phosphorus in 

 iron and steel, the sample is dissolved in nitric 

 acid, oxidized with permanganate, the excess 

 being removed by means of oxalic acid, ammo- 

 nium nitrate is added, and the phosphoric acid 

 precipitated by means of molybdic solution. 

 The phosphomolybdic precipitate is centrifuged 

 and the volume read off by means of gradu- 

 ations on the tube ; with the aid of a table, the 

 percentage of phosphorous may be ascertained. 



Third. — Examination of sputum for presence 

 of Bacillus tuberculosis. The expectorated matter 

 is mixed with its equal volume of hot water, or 

 a dilute aqueous solution of borax, then heated 

 for ten minutes on a water-bath, agitating re- 



peatedly. The mixture is then centrifuged and 

 the fluid is decanted off from the precipitate, 

 which is then examined. 



Fourth. — Examination of milk for Bacillus 

 tuberculosis. 20 Cc. of the sample of milk are 

 mixed with i Cc. of a 50^ solution of potassa, 

 warmed for two minutes on a water-bath, until 

 the fluid has taken on a yellow brown color, 

 then 20 Cc. of glacial acetic acid are added, 

 shaken and heated again for three minutes on 

 a bath. The fluid should then be of a uniform- 

 ly smooth consistency and free from flocculent 

 matter. This is then centrifuged. Any of the 

 bacilli present will settle in the bottom of the 

 tubes, while the butter fat swims on the surface 

 of the mixture. The fluid is decanted off from 

 the sediment, to which is added 40 Cc. of hot 

 water and the mixture again centrifuged. After 

 decanting the clear supernatant fluid, the sedi- 

 ment may be examined with the microscope. 



Fifth. — Separation of urinary sediments. 50 

 Cc. of the sample of urine is centrifuged and 

 the sediment examined. 



Sixth. — This same process may be employed 

 for the microscopical examination of substances 

 which cause the turbidity of beer, wines, 

 liquors, etc. 



Seventh. — For the separation and examina- 

 tion of suspended matters as infusoiiH, algae, 

 etc., in drinking water. Usually 50 Cc. of the 

 sample of water are selected. For identifying 

 typhus or cholera bacilli 100 Cc. of the water 

 are shaken witho. i Gm. of the finest levigated 

 talc (sterilized) and centrifuged. The talc 

 serves the purpose of assisting the rapid separa- 

 tion and collection of the bacilli in the bottom 

 of the tubes. 



Eighth. — For the determination of fats in 

 milk, 10 Cc. of an average sample are placed in 

 a tube of the centrifugal, i Cc. of a 50 per cent, 

 solution of potassa added, and mixed by rota- 

 tion; then warmed two to three minutes on a 

 water bath, until the mixture takes on a more 

 or less brown color; it is then again rotated and 

 glacial acetic acid added, until the caseine is 

 dissolved. It is again warmed and centrifuged. 

 The amount of fat is simply estimated by read- 

 ing its volume. 



Ninth. — For estimating the percentage cream 

 in milk. 20 Cc. are centrifuged and the volume 

 read off by means of the graduations on the 

 tube. 



Tenth. — For determining the fatty acids in 

 soaps, a weighed amount of the soap is dis- 

 solved in water in the centrifugal tube, an acid 

 (H^SO_t) is added, and the mixture centrifuged, 

 after which the amount of fatty acids may be 

 read off. V. C. 



