W. H. Dunnigan and partners opened the Purity Dairy and the Purity Apartments (upstairs) in this brick commercial building in 1916. Purity was the first dairy processing plant in Anaconda to pasteurize raw milk brought in from area farmers. French microbiologist Louis Pasteur developed the process of heating liquids to kill harmful bacteria in 1864, but commercial milk pasteurization equipment was not available until 1895. Following a 1913 New York City typhoid epidemic resulting from contaminated milk, public health officials called for stringent milk pasteurization laws. Though most cities—including Billings—had, by 1917, mandated that milk be pasteurized, some small-town dairies resisted because the machinery was expensive. Nevertheless, Purity brought in the latest pasteurization machinery along with a factory specialist from Chicago’s Davis Milk Machinery Company. Purity touted its “safe milk” in newspaper ads and invited customers to observe their process through the large storefront window and on guided tours. Its marketing effort paid off. After just one month in operation, the dairy reported six hundred new customers. It remained at this location, with various owners, until 1962.