Ah the old original mechanical foam concentrate - protein foam.
If you got the concentrate on normal clothes it was a s*d to get the smell & stain out.
"Protein compounds are prepared by the chemical treatment of various protein materials & when suitably diluted with water they enable stable foam for fire fighting purposes to be produced....the basic materials used in the manufacture of protein compounds are horn & hoof meal, or animal blood. During the course of manufacture of horn & hoof meal a certain amount of acid is used and in early type of this manufacture, sulphuric acid was employed. Compound made by this process tended, in course of time, to the formation of sludge, which consisted mainly of crystals of calcium & sodium sulphate. This compound, referred to as a 'sulphate compound' is not now manufactured. To overcome the sludging problem, hydrochloric acid is now used and this compound is known as 'chloride compound'. This, like the compound manufactured from animal blood, is virtual sludge free......."
Manual of Firemanship Part 1:1963
This link gives the ingrediants of 'P' foam which is still made today:
http://www.angusfire.co.uk/GetFile/F3E8271F9642A56480256DA4004D6085/F01-01n2.pdfSodium Chloride and Glycol compounds are the main ingrediants after the protein source
