86 JOURNAL OF THE 



FILTERS WASHED WITH HYDROFLrORIC ACID. 



The removal of silica from filters by washing with hydrofluoric 

 acid was first recommended by Austen (Zeitschr. x\nal. Chem.). 

 Acting upon this suggestion, Schleicher & SchuU have prepared 

 since Spring of 1883. filters washed with both hydrochloric and hy- 

 drofluoric acid. An .lamination of these filters shows that the ash 

 can in most cases be disregarded. The published analysis gives the 

 ash of a 11 c. m. filter as 0.00017 grm. Burning five and weighing 

 on a fair balance gave 0.0002 as the weight of one ash. They are a 

 little difficult to burn thoroughly. The average weight of the dried 

 filter, same size, is 0.6284. The washing with hydrofluoric acid has 

 decreased to a slight extent the power of retaining fine precipitates. 

 The unwashed paper of the same number and grade fail to catch 

 such a precipitate as calcium oxalate, even after standing several 

 hours, that is, the first few drops are turbid. With the washed filters 

 the turbidity is greater and more lasting. Several sets of experi- 

 ments were carried out with papers from different packs, some pro- 

 cured from Germany, some from the New York agents, and it was 

 found that all ordinary difficult precipitates except calcium oxalate 

 were retained when the proper precautions were taken, the filtrate 

 running through with great rapidity. The folding of the filters 

 must be done carefully, as they break somewhat easily. The filter 

 fibres, too, are apt to rub off. When accurately fitted, with a plati- 

 num cone, to a funnel in a filtering flask, they were found to stand 

 well the pressure caused by an ordinary water air-pump. The head 

 of water was about twenty-five feet. The advantages of these filters 

 then are the rapidity of filtering and the extremely low ash-weight. 

 The disadvantages are the ease of breaking and the necessity of care 

 to prevent the passage of certain fine precipitates. 



Chemical Laboratory, U. N. C. F. P. Yenable. 



OCCURRENCE OF ABIES CANADENSIS AND PINUS 

 STROBUS IN CENTRAL NORTH CAROLINA. 



Abies Canadensis, MirJix. (Hemlock Sjjruce). —in many parts of 

 the mountain region of North Carolina this tree occurs in consider- 

 able abundance— especially in the mountain valleys, along the bor- 

 ders of streams and swamps; and it has been observed about the 

 base of mountains at some distance east .of the Blue Ridge proper. 

 So far as I am aware, how^ever, it has not been recorded as occur- 

 ring at any point east of the ' ' Mountain Region. " Recently ) was 



