Sorrry didn't mean to be so curt, had to get "my big old wife" of to work!
What Woody said. The small bottles are fine if you need something portable and want to carry it out to do a small job. But in the shop TIG welding your going to use 10-15 cuft of gas on the average. Most of your suppliers will have cylinders from 20 to 380 cuft. A Linde-style T, 380-cubic-foot cylinder would give you around 25 hours of welding time and a mid sized, say 150 cuft bottle would give you about 10 hours. You can see that the smaller tanks are only going to give you an hour or two of welding time before you have to get a refill.
And Woody, I'm sure you've found out by now that the others are quite correct, you need an inert or noble gas to maintain the plasma for the arc in TIG welding. MIG is generally a short circuit process unless your using the spray arc process in which case you would be using a 95/5 or 98/2 argon/co2 gas.
Denny Graham
Sandwich, IL
