Development of standards for analytical filter papers.

Filter papers used for ordiuar.v q uali tative and q uant itative analyses were treated to obtain data for recomnlencted standards of Cjuality. The papers comprised the produ cts of two domestic and three foreign manufacturers. T ests were made for retention of fine precipitates, t im e of flow of water , ash, and wet bursting strength by m odi fi ed methods developed at the Bureau. Den sity, alpha-cellulose, copper number, and acidi ty were also determined . Instances of filter paper becoming too brittle fo r use th rough deteri oration h ave been observed. Stable papers are characte ri zed by a high content of alpha-cellulo e, a low copper n um be r, and low acidity. Furthe rmore, the degraded cellulose of de teriorated fil ter papers may cause erroneous analytical results . The ash, bursting strength, den sity, and time of fl ow of II'ate r varied considerably for papers made for the same s taled use. The alpha ce llulose con tent and copper number also varied considerably in papers made by diffe rent manufacturers. The acidity of all the papers was low. The papers showed a correlation between density and time of flow of water. Data are given showing the much greater decrease in alpha-cellulose and increase in copper Ilumber of papers of poor condition of cellulose t h an of papers of good Cjuality of cellulose when subj ected to accele rated aging. Data are also included on the poor cond iti on of cellulose in deteriorated paper as compared with paper t lutt had not de te riorated. Degraded cellulose is solu ble ill alkaline solu t ions and to some ex tent in water, and examples are given of how this may affect analyses. R ecommended standards are given for the properties considered of the most import ance: a lpha-cellulose, copper number, ac idi ty , ash, bursting strength, and t ime offiolY of water .