LABORATORY SUPPLIES AND CHEMICALS 145 



2713 FILTER PAPER, Whatman No. 42 (S. & S. No. 589 s , Blue Ribbon), a double- 



acid-washed paper, similar to No. 40, but much harder and 

 extremely close in texture. On account of its close texture 

 it is recommended for use with the filter pump and as folded 

 niters where possible. Especially adapted for the finest pre- 

 cipitates which tend to pass through the filter paper, such as 

 Barium Sulphate when precipitated in cold solution, and in 

 general for precise analytical work where speed is not im- 

 portant. 



Diameter, cm 7 9 11 12.5 15 



Per 100 circles $1.20 1.70 2.00 2.30 2.70 



2714 FILTER PAPER, Whatman No. 43 (S. & S. No. 589*, Yellow Ribbon), a double- 



acid-washed paper, of the same stock as No. 40, but having 

 been subjected to an additional chemical process which renders 

 it fat-free. Especially suited for the recovery of the ether 

 extract in the Roese-Gottlieb Fat Test, and in general for 

 any purposes requiring a fat-free paper. 



Diameter, cm 7 9 11 12.5 15 



Per 100 circles $1.50 2.20 2.55 2.80 3.60 



2715 FILTER PAPER, Whatman No. 44 (S. & S. No. 590), a double-acid-washed 



paper of thinner substance and lower ash content than the 

 preceding numbers. It will retain the finest precipitates, but 

 is slightly slower in filtration than No. 40. No. 44 is recom- 

 mended for use when the greatest possible degree of accuracy 

 in quantitative work is required. 



Diameter, cm 7 9 11 12.5 15 



Ash weight per circle 



grams 00003 .00005 .000077 .00001 .00014 



Per 100 circles $1.50 2.20 2.55 2.80 3.60 



2715a FILTER PAPER, Whatman No. 50 (S. & S. No. 575), a paper specially hard- 

 ened by treatment with Nitric Acid. Very tough, will 

 resist great pressure, and retain the very finest precipitates. 

 Can be used repeatedly, the hard smooth surface permitting 

 precipitates to be scraped or washed off without injury to 

 the paper. Especially recommended for use with vacuum. 

 Suitable for very fine precipitates and for filtering corrosive 

 liquids such as Acids and strong Alkalies. Should be used 

 when it is desired to transfer a precipitate without ignition. 

 Widely used for filtering Biological products, as the hardened 

 surface prevents contamination of the filtered product by 

 particles of paper when scraped off. Can be used as a sub- 

 stitute for platinum cones, and as supports for large folded 

 . filters to prevent them bursting at the points. 



Diameter, cm 4% 5 l / 2 7 9 11 12.5 15 18% 24 32 50 



Per 100 circles $0.55 .90 1.20 1.70 2.00 2.30 2.70 3.60 6.10 11.35 20.85 



Orders less than $100.00, list prices Strictly Net 



Orders amounting to between $100.00 and $200.00 list prices 5% 



Orders amounting to over $200.00 10% 



For institutions of learning we can arrange Special Duty Free Importations of 



Whatman Filter Papers upon the condition that all necessary Government requirements 



are complied with. Full information upon request. 



2715b FILTER PAPER, Celeritas (S. & S. No. 588), Folded, excellent quality, free 



from chlorine, folded in such a way as to protect the points 

 from tearing. In boxes of 100 filters. 



Diameter, cm 12.5 15 18.5 24 32 50 



Per box of 100 $1.50 1.80 2.25 3.00 5.00 7.50 



2715c FILTER PAPER, Grey, French, Prat-Dumas make, size, 17x22 inches. 



Ream, 7.50 quire $0.40 



Circular, put up in packages of 100 sheets. 



Diameter, cm 10 125^ 15 19 25 33 40 45 50 



Per 100 sheets. . .$0.20 .30 .40 .66 .92 1.40 1.72 2.40 3.00 



