Within a year of Brearley’s discovery, Krupp in Germany was experimenting by adding nickel to the melt. Brearley's steel could only be supplied in the hardened and tempered condition; the Krupp steel was more resistant to acids, was softer and more ductile and therefore easier to work. There is no doubt that but for Brearley's chance discovery, the metallurgists at Krupp would have soon made the discovery themselves. From these two inventions, just before the First World War, the "400" series of martensitic and "300" series of austenitic stainless steels were developed. The First World War largely put a halt to the further development of stainless steel, but in the early 1920s a whole variety of chromium and nickel combinations were tried including 20/6, 17/7 and 15/11. Brearley’s successor at the Brown Firth Laboratories was Dr W.H. Hatfield, who is credited with the invention in 1924 of 18/8 stainless steel (18% chromium, 8% nickel) which, with various additions. Today 18/8 is comanly known as 304 and still dominates the melting of stainless steel today. Dr Hatfield also invented 18/8 stainless with titanium added, now known as 321.