In August 1924, William Kroll acquired a splendid double-villa in the Luxembourg-city suburb of Belair. The price paid for this property amounted to LUF 250,000, a large sum for a 35-year-old engineer who had only started earning a salary in 1918. Inevitably, the question arises as to how Kroll obtained the funds for the purchase of this villa in Belair. 

The answer is: Kroll was a successful inventor and he protected his inventions through patents which he licensed or sold.

Although Kroll did not leave much information on his financial situation around 1924, it emerges from various publications that around 1917 Kroll had filed patent applications in Germany in his own name, prior to taking up employment with Metallbank & Metallurgische Gesellschaft A.G. (M&M), which patent applications were to become of great commercial interest. The patents were granted in 1923, respectively 1925 and related to the following subjects:

•  Process for preparing lead-based bearing alloys (so-called “Lurgi-Metall” or “Bahnmetall”)

•  Process for removing bismuth from lead (later known as “Betterton-Kroll process”)

The first invention allowed the production of lead bearings without additional nickel and was the result of a joint effort of several engineers, including William Kroll and Polish chemist Jan Czochralski, and was commercialised by M&M [1] under the name of “Lurgi-Metall”. 

Kroll joined M&M in 1918 and assigned his patent rights to his employer (as evidenced by the granted patents) from whom he received royalty fees at least up to 1941 [2]. Some authors [3][4] suggest that he also received a substantial up-front payment.

The “Betterton-Kroll” process made it possible to remove bismuth from lead and thereby to refine lead for industrial use. Kroll’s patent rights were bought by the company American Smelting and Refining Co around 1923 [5], again suggesting that Kroll received at the time a substantial payment.

The financial rewards from his 1916/1917 inventions (up-front payment and/or royalties) must have allowed Kroll to buy the property in Belair and to set up his laboratory there in 1924.

In later years Kroll obtained patents in other fields, which allowed him to continue his work as an independent researcher. For example, he licensed his patent for a “Process for the production of metallic beryllium” (US Patent No 1,740,857) around 1929 for a royalty fee of 4%. [6]

Unfortunately, Kroll’s most valuable invention (the industrial process of producing titanium), made in 1937, brought him final financial rewards only at a very late stage of his life, namely in 1962, when he was already retired and aged 73. 

Kroll learned early in his life that it was wise to protect inventions by patents. During the years 1910 to 1917 he worked as an assistant to Professor Walther Mathesius at the Berlin-Charlottenburg Technische Hochschule. Judging from the number of patents filed by professor Mathesius in Luxembourg, the latter must also have taught Kroll the importance of protection of inventions through patents. [7]

Three of William Kroll’s brothers, François [8] , Adolphe Maria Victor [9]  and Paul [10], all three engineers, also obtained patents in Luxembourg.


[1]  Katrin Steffen, Wissenschaftler in Bewegung: Der Materialforscher Jan Czochralski zwischen den Weltkriegen, Zeitschrift für moderne europäische Geschichte (2008), pp. 237-261 

[2] Archives nationales, cote AE-AW-0457

[3] Robert Stumper, d’Lëtzeburger Land, No 15, 13 April 1973, page 4

[4] Helmut Maier, 100 Jahre Deutsche Gesellschaft für Materialkunde (2019), p. 12

[5] Helmut Maier, 100 Jahre Deutsche Gesellschaft für Materialkunde (2019), p. 12

[6] “Prior to 1934, Kroll granted S & H exclusive rights in an invention in the beryllium metal field for a royalty rate of 4 percent, and exclusive rights to utilize the Kroll copper-titanium patents for a royalty rate of 5 percent.”. - Henry A.Carey, Jr., Edwin D.Hicks, J.Pierre Kolisch and Joseph Schulein vs The United States, Report of decisions of the Supreme Court in Court of Claims cases, 1964, page 331 

[7] Prof. Mathesius obtained, for example, 9 patents in Luxembourg during the years 1904 to 1935: LU 5458 (1904), LU 7351 (1908), LU 7356 (1908), LU 8371 (1910), LU 8372 (1908), LU 9265 (1911), LU 9266 (1911), LU 16472 (1929), LU 21391 (1935)

[8] LU patents No 8,017 and No 13,624

[9] LU patents No 9,973, No 19,335, No 20,568, No 31,641 and No 32,252

[10] LU patents No 12,261, No 14,246 and No 16,949; DE patent No 357,966