William J. KROLL, the inventor

Luxembourg period (1889 - 1939)

Table of contents


Chronology of William Kroll’s patents                                                                

‍        Lead-calcium alloys                                                                                                

‍        Process for the separation and recovery of metals from metal alloys                        

‍        Process for preparing alkaline-earth metal alloys                                                    

‍        Process for desulferising iron and steel                                                                        

‍        Si-Al alloys (Alusil and Alsia)                                                                                

‍        Iron, nickel, beryllium alloys                                                                                

‍        Copper, titanium alloys   

‍        Titanium   

‍        Manganese-base alloys   

‍        Zirconium   

Kroll’s US patents   

‍        Introduction   

‍        Contracts between Kroll and Siemens & Halske   

‍                1930 contract   

‍                1934 contract   

‍        The complicated life of Kroll’s US patent applications and patents   

‍                Vesting orders   

‍                        Order 1   

‍                        Order 2   

‍                        Order 3   

‍                        Order 4   

‍                        Order 5   

‍                Appeal by Kroll   

‍                Life of the patents after the vesting orders   

‍                        The “Nickel alloy” patent (US 1,986,585)   

‍                        The “Titanium” patent (US 2,205,854)   

‍    Final note   

Addendum 1   

‍        The file history of the “Titanium” patent (US 2,205,854)   

Addendum 2   

‍        William KROLL’s patent portfolio   

Addendum 3   

‍        William KROLL’s publications   

Addendum 4   

‍        Medals and honours   

Addendum 5   

‍        “Kroll” as a trademark   


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 1965, when he was already retired and aged 76. 

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.

Chronology of William Kroll’s patents

Since Kroll published his own biographical note in 1955 [11], quotes from this publication will be used hereafter in the context of his patent portfolio.


“The laboratories of the Technische Hochschule in Charlottenburg, Germany, where I studied iron metallurgy from 1910 to 1917, were well equipped with all sorts of furnaces. I spent the years of the First World War there as an assistant to the professor of iron metallurgy, W. Mathesius, and worked on my doctoral thesis under K. A. Hofman on the production of pure boron.”


Kroll, still doctoral student at the Technische Hochschule in Berlin-Charlottenburg, was in the process of finishing his thesis on the production of pure boron, a study he had started in 1910 under Professor K. A. Hofman. At the same time, he started investigating lead alloys under Professor W. Mathesius. 

Kroll’s interest was directed towards developing, in general, a process for making alloys of the alkaline-earth metals. [12]

Kroll’s first patent related to calcium-lead alloys followed by a second patent relating to barium-lead and strontium-lead alloys.

The barium-lead alloys, in particular, became of great importance to the German railway industry during World War I, when they were used for making bearings.

The German company Metallbank & Metallurgische Gesellschaft A.G. (M&M), later called Metallgesellschaft [13], was engaged in 1916 in developing these bearings, which later received the name of “Lurgimetall”. 

“Lurgimetall” is a lead-based alloy, nominally containing 96.3-97.3% lead, 2-3% barium, 0.4% calcium, and 0.3% sodium. 

The following table lists the main patents relating to the “Lurgimetall” technology owned by M&M, including the two patents specifically designating Kroll as inventor. The patents are arranged in chronological order according to their filing dates. 

Lead-calcium alloys


[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

[11] Journal of the Franklin Institute, Vol. 260, September 1955, pages 169-192

[12] beryllium, magnesium, calcium, strontium, barium, and radium

[13]“Metallbank A.G.” and “Metallurgische Gesellschaft” merged in 1910 and became ”Metallgesellschaft” in 1928

(to be continued)