WOW - what a find. You are very lucky to have found it. If it were mine, I would not try the snow.
I used to work in a quilt store and we sold little packets of something for this purpose but I can not remember what it was. I went googling to see if I could find it and found this link
http://www.home-ec101.com/how-to-cle...intage-linens/
I also found the detergent that they were talking about at Amazon
http://www.amazon.com/Restoration-Hy.../dp/B002ISCPD2
I myself have not tried this detergent, but if it were mine I would aim for using something that was designed for this purpose.