I have 5 Ni-Cd battery(1.2V 2200mAh). They connected in series. I have a 19 V 3.42 A adapter. Will it make a problem when I charge Ni-Cd batteries with my 19 V adapter? Is 19 V dangerous for charge Ni-Cd batteries?
19V would be too much for your NiCd. I don't recommend doing this.
You can typically charge NiCd at about 1 C/hr; in your case, 2.2 A max. With 19V-6V overvoltage, you'll potentially fry the batteries pretty quickly. This is acutely dangerous. You don't want fire mixed with cadmium. Bad combination.
Get a charge controller. Or simply, a charger.
If you were to fill a water ballon from a faucet, you wouldn't turn the faucet on all the way. You also would want to stop when the balloon reached a certain size. And you would not turn the water on and walk away. These essential controls are the same needed for charging batteries. You need to control how fast they charge, and know when to stop. So, there is a piece missing from your proposal--a charge controller.
This is a good question, in the sense that everyone who gets into electronic design needs to understand what they are attempting before they start asking about how to do it.
You can do it, but you need to be very careful.
To start, the standard NiCd charge technique (for a fully discharged battery) is 16 hours at a 0.1 C rate. C is the battery capacity. So, for instance, if you have 2200 mAhr cells, you can charge at 220 mA. The trick is knowing when to terminate charge.
You can try this. Take your batteries and discharge them completely. Discharge each cell seperately, not in series. Now connect them in series. Find the resistance needed to get the proper charge current. Now start charging. Wait 16 hours. Measure the battery voltage and record it.
Now you can charge your batteries even if they are not fully discharged. Just stop when the voltage reaches the cutoff voltage which you recorded. However, be aware that you'll need to check the battery voltage at least once per hour.