87a - Frédéric HOFFMANN (1818 - 1900)

Friedrich Eduard HOFFMANN was Königlicher Baumeister (Architekt) in Berlin and the inventor of the Hoffmann’scher Ringofen [1] or, in English Hoffmann kilns [2], patented and used throughout the world in the 1860s. The original title of the invention was : « Ringförmiger Ofen zum ununterbrochenen Betriebe beim Brennen aller Arten von Ziegeln und Tonwaren, Kalk, Gips und dergleichen ».

HOFFMANN held patents in Austria, Prussia, Great Britain, Belgium, Italy, Netherlands, France, Norway, Sweden, Finland and Russia, all obtained between 1858 and 1869.

In Luxembourg, HOFFMANN filed his application for a brevet d’importation on 29 December 1865 under the title of:

Système de perfectionnement de fourneaux 

The corresponding US patent explains: [3]

This invention consists in an endless arch or channel divided into a series of distinct sections, each of which is provided with openings for introducing the fuel and the material to be burned, and communicates through a radiating flue with an annular smoke-chamber, in combination with suitable slides or movable partitions, and with a smoke-stack communicating with said annular smoke-chamber by four (more or less) passages in such a manner that brick or other material introduced into the several sections of the kiln can be gradually heated and cooled, and the operation of the kiln can be continued for any length of time with great economy in fuel.

The Chambre de commerce was instructed, as usual, to examine the application. Experts Frédéric FISCHER and  J. H. MICHEL conducted the examination and reported on 14 July 1866 to the Chambre de commerce:

(drafted in old German handwriting, still to be transcribed)

On 25 September 1866 the Chambre de commerce, in turn, made the recommendation to the Government to reject the patent application:

… Nous avons fait examiner ces pièces par les experts M.M. Fréd. Fischer, chimiste à Luxembourg et J. H. Michel, mécanicien à Eich, lesquels, dans leur rapport ci-joint, ne reconnaissent pas à ce système, ni le mérite de la nouveauté ni de perfectionnement du procédé utilisé dans notre pays; ils déclarent en outre comme dangereux l'usage desdits fourneaux, pour autant qu'ils en ont pu juger par la description incomplète de l'impétrant. 

En conséquence, nous sommes d'avis qu'il n'y a pas lieu d'accueillir cette demande et avons l'honneur de vous retourner les pièces.

The Government refused the grant of a patent. [4]

Final note

This decision is remarkable in retrospect since the HOFFMANN invention represented, at the time, a major advance in the brick-making industry. Licences of the patent were granted worldwide and even infringers of the patent were brought to court in Italy.

However, the patents in Prussia and in Hessen were invalidated in 1870, after 10 years of their existence, on the basis of lack of novelty (invention used in 1839 for a short time by Arnold in Fürstenwalde). 

Carl REULEAUX who wrote a 70 page booklet on this case in 1873 took the view that the revocation action of the patent was  politically motivated and based on bad faith.


[1] Wikipedia DE

[2] Wikipedia GB

[3] US patent No 48,244

[4] It is to be noted that the patent application, although it was fully processed, was not recorded in the Register of patent applications.