The 78 record

In 1900, 78 records arrived on the scene.  These 10 inch records were easier to store and had very large grooves (much larger than both 45s and LPs). This 10 inch record only holds about 4 minutes of music per side.
Though these records were a vast improvement to the cylinders, they were still heavy, fragile, and just couldn't hold enough material, they disappeared in 1960.  Most 78s play back at about 78.26 RPM.
Emil Berliner (inventor of the gramophone) did a thorough study of these records and determined that the most pleasing speed for playback was roughly 78 Revolutions Per Minute.   Because his British Gramophone company had established the record format, others followed suit and 78 RPM was established.
Playing 78rpm Records
Simply playing a 78rpm record is not so simple these days.  Your modern turntable likely doesn't even have a 78rpm setting on it.  You likely don't have the correct stylus for these records AND if you play them thru your modern stereo system, they will not sound right. 
Stylus   
 this is the needle used to play the records.  Your preset cartridge and stylus is almost certainly about .7 Mills in size - which is perfect for 33 1/3 LPs.  78s were recorded with groove widths about 2.5 Mills in size - they are over 3 times wider!  You can play an occasional 78 with your regular LP stylus, but it won't sound as good.
Acetate recordings are often covered with a white coating that appears as a powdery substance on their surface.  This material (hexadecane acid) is not soluble in H2O.  It is suggested that records with this problem be cleaned using distilled H2O for the best transfer.  Do not attempt to use solvents to remove the acid.

- Marius Oosthuizen, SABC Radio Archives