Alessandro Cruto

Biography
The Cruto lamp was manufactured in Europe and is, therefore, not well known in the United States. The inventor, Alessandro Cruto, likewise is not a familiar figure in lamp history that is written in the United States. A biographical sketch of Cruto is therefore in order and the write-up by Frank Andrews⁸"Alessandro Cruto was born in Italy on 18th March 1847. He studied chemistry in Turin and became interested in the idea of making diamonds in the laboratory by the crystallisation of carbon. In September 1873 he produced a layer of dense carbon hard enough to scratch glass. But it was not his expected result and he studied the new material for many years.

At a conference on electric lighting in May 1879 he realised that his material was suitable for use as a filament in an incandescent lamp. His first lamp had a filament measuring 12 x 3 x 0.52 mm and gave a bright light. But the efficiency of this lamp was low. By September 1881 he had achieved a successful version of this the first synthetic filament. He formed A. Cruto & Company in February 1882 with very limited backing and had to develop all his own manufacturing methods.

After seeing a Swan lamp he realised that he had to reduce the surface area of his filament, but due to the impurities present found this to be unsuccessful. He then applied his process to platinum wire, changing the process to create a chemical bond between the carbon lamination and the platinum. The platinum wire was then evaporated by passing a high current through it. This bulb was successful and fell outside the scope of the Edison-Swan patents.

Unfortunately the limited finance he had obtained prevented him competing against the rich Italian Edison Company. Edison had installed a thermo-electric power station in Milan in 1883 and supplied all the bulbs used on the system.

The Cruto bulb was exhibited at the Munich exhibition in 1883. Cruto managed to stay in business but only in a limited way, and due to management problems he left the company in 1893. At some stage it appears that the Cruto company may have switched to a standard type of filament. Cruto bulbs were sold in France under the name SYSTEME CRUTO. These were fitted with a bayonet cap and had a single horseshoe shaped filament. He died in 1908." According to Heerding⁶, in 1890, Cruto lamps were manufactured in Paris, France by Société de Soudure Electriques des Métaux, in Milan, Italy by Rivolta & Co., and, in Turin, Italy by Società Italiana di Elettricità, Sistema Cruto. Apparently bases other than the Cruto were used as time passed. In addition to the Heisler base, pictured above, in 1896 it is believed the Ediswan base was also used⁵. An article from The Electrical World³ follows:

"Among the incandescent lamps at the Philadelphia Electrical Exhibition (in 1884), the 'Cruto,' of French manufacture, though not in operation, attracted attention on account of the high claims of efficiency made for it. The construction of this lamp is peculiar. The main object, as in others, is to obtain a filament of the greatest possible homogeneity. The method employed to effect this is quite original and is described in a recent number of our French contemporary, L'Electricien. M. Cruto builds up his filament little by little, and thus obtains a carbon of great density, the pores of which are small as possible.
"The process employed depends upon the fact that certain hydro-carbons are decomposed by heat, and their carbon deposited upon the heating surface. This is the method usually employed for standardizing carbon filaments, as they come from the carbonizing furnace.
"In the present instance the carbon is deposited on a core of platinum raised to incandescence by the passage of a current while in the midst of a hydro-carbon gas.
"The platinum employed is very fine, being only 1/100 millimeter (about .0004 inch) in diameter, and is produced by means of the Wollaston process. This process consists in drawing a silver wire with a platinum core to a very small diameter, and then dissolving the silver in an acid which does not attack the platinum; this leaves a very fine platinum wire. The wire thus made is cut into lengths of 150 millimeters (6 inches) for the 16 c.-p. lamps, and then stretched on a form which gives it a U shape. After this the ends of the wire are placed in two clamps in circuit with a dynamo; the clamps are mounted on a base which forms the stopper to a glass jar. Hydro-carbon gas is admitted through a tube passing through the stopper, and the deposition of carbon takes place in the jar.
"The gas employed here is bicarbonate of hydrogen, produced by the action of sulphuric acid on ethylic alcohol. This gas, after being washed and dried, is stored in a reservoir, whence it is drawn as required.
"In order to produce the deposit of carbon, the jar is filled with gas, and a current is sent through it, of about 150 volts E.M.F.; in order to protect the filament, however, a rheostat is put into the circuit so that the current can be regulated. At the beginning, the resistance of the platinum wire is 350 ohms, but at the end the filament is reduced to 150 ohms. During the process a curious fact is noticed; at the end of five or six minutes the resistance of the filament suddenly increases, and then decreases regularly during the time of formation, which varies from 1 1/2 to 2 hours.
The reactions which take place in the glass jar are very complex, and after three applications the jar must be cleaned. This becomes necessary on account of the deposit of carbon which settles on the walls of the jars and prevents any observation of the interior. As the deposit of carbon proceeds, the interposed resistance is gradually diminished, and the gas renewed from time to time.
"The current has, in addition, a mechanical action on the platinum wire; thus, a repulsion of the two branches of the loop is observed, and a tendency to take up a certain cardinal position. In order to avoid this tendency, the two sides of the loop are placed in the same plane of the magnetic meridian. If the loops become crossed during the operation, they are brought back to their original position by reversing the direction of the current.
"The filaments so formed are then inserted into the platinum ends forming the terminals of the lamp, and cemented to them by a similar deposition of carbon. This process, it is claimed, gives a most dense and homogeneous filament, and the efficiency of the lamps, according to published accounts, exceeds that of the other lamps which have thus far come into general commercial use. The process is an ingenious one and could be applied in more than one way."

There are six Cruto lamps listed in the William J. Hammer Historical Collection of Incandescent Electric Lamps : lamps 1883-24, 1883-38, 1883-505, 1884-521, 1897-1009 and 1902-1029). It appears, therefore, that Cruto lamps were definitely manufactured during the 1883-1902 time period.