Vintage 1930's or earlier German Waschblau blue wash balls for making your linens appear more white. Instructions translate to: Hold one of these blue balls in between 2 fingers or in a cotton bag, swirl it in a tub of water until it is sufficiently blue (don't dissolve the entire ball) and the blue color will counter the yellowing of your white cloth and make them appear more white again.
It was the a more gentle alternative to bleach. The price is for one full packet (10-12 balls) and one sample packet that contains 1 ball. Interesting home front item.