Examples of scientific discoveries made by trial and error?

The classic example of work done by trial and error is the light bulb. The workers in Edison's lab tried hundreds of different materials for use as a filament before tungsten wire was tried.

The discovery that saccharin makes a good artificial sweetener was made quite by accident. (In checking the spelling of saccharin, I found this website on the top ten accidental discoveries. You may find it useful. http://science.discovery.com/brink/top-ten/acciden...

I would not consider Rutherford's explanation of the alpha scattering experiments to be either "trial and error" or "accidental". The experimental work done by Geiger and Marsden was well thought out and very thorough. The fact that they observed alpha particles scattered through large angles was unexpected but they test for them just the same. The large angle scattering was found because they looked for them. It was neither accidental nor trial and error.

To the best of my knowledge penicillin was found by chance, not trail and error. (A scientist left a petri dish of bacteria over night to test something, but when he came back in the morning the bacteria was dying due to penicillin g being present.)

Relenza, which helps cure influenza, was made by trail and error as far as I know.

Another one, although i'm not too sure of this, was nuclear fission. However you may want to research this before you accept it as fact.

This article seems to imply that it was found by chance

http://en.wikipedia.org/wiki/Nuclear_fission#Disco...

The alchemist worked with 14 elements: sulfur, mercury, carbon, iron, lead, copper, tin, silver, gold, phosphorus, arsenic, antimony, bismuth and zinc. Although the failed to transform lead into gold and met with limited success in their other endeavours, they accumulated a body of knowledge of how different chemicals react and developed a range of experimental techniques

Faraday and his work on electrolysis, and electricity generation, and storage.

Newton and gravity.and light