THE ARSENIC CONTENT OF FILTER ALUM [with DISCUSSION]

It is well known that products which are manufactured with the aid of commercial sulphuric acid quite generally contain more or less arsenic, depending upon the purity of the acid used. The poisonous character of arsenic compounds, even when present in small amounts, makes it of general interest and importance to have definite knowledge of the presence or absence of arsenic in any substance which enters directly or indirectly into foods or drinks. Sulphuric acid is used in the manufacture of filter alum and it is therefore quite essential, particularly to those who are in public health work, to know whether arsenic in any considerable amounts is being added to drinking water in the process of purification with alum. We have been unable to find any definite published data relating to the arsenic content of filter alum. Dr. George A. Soper several years ago made an investigation of this problem, and referred to his results while discussing a paper by Mr. E. E. Wall2 on "Water Purification at St. Louis, Missouri." Dr. Soper was discussing in par-