On 29 July 1940, manufacturers Albright & Wilson of Oldbury demonstrated to the RAF how their white phosphorus could be used to ignite incendiary bombs. The demonstration involved throwing glass bottles containing a mixture of petrol and phosphorus at pieces of wood and into a hut. On breaking, the phosphorus was exposed to the air and spontaneously ignited; the petrol also burned, resulting in a fierce fire. Because of safety concerns, the RAF was not interested in white phosphorus as a source of ignition, but the idea of a self-igniting petrol bomb took hold. Initially known as an A.W. bomb, it was officially named the No. 76 Grenade, but more commonly known as the SIP (Self-Igniting Phosphorus) grenade. The perfected list of ingredients was white phosphorus, benzene, water and a two-inch strip of raw rubber; all in a half-pint bottle sealed with a crown stopper. Over time, the rubber would slowly dissolve, making the contents slightly sticky, and the mixture would separate into two layers – this was intentional, and the grenade should not be shaken to mix the layers, as this would only delay ignition. When thrown against a hard surface, the glass would shatter and the contents would instantly ignite, liberating choking fumes of phosphorus pentoxide and sulfur dioxide as well as producing a great deal of heat. Strict instructions were issued to store the grenades safely, preferably underwater and certainly never in a house. Mainly issued to the Home Guard as an anti-tank weapon, it was produced in vast numbers; by August 1941 well over 6,000,000 had been manufactured.