DS1820 bad reading from 4th sensor
Max current

For 4 sensors I wouldn't expect problem, however, for 50 it will.
The VCC/GND pin has a maximum of 200 mA, see Arduino Pin Current Limitations.

(Update after remark of Gerben, thanks!):
However, these are for the ATMega, not the Arduino R3. See Arduino Voltage and Current. It's not an official document, but made by Gabriel Staples). It contains a lot of references. But the VCC can handle 0.5 or 1A depending on USB or battery power. 

This means:
The DS1820 uses 4 mA (checking a random datasheet), so 50 * 4 = 200 mA, which is way within 500 mA/1000 mA).

Non one wire sensors (not your case)

Since you have one wire sensors the following is not applicable (just leave it here for others):

None one-wire sensors use their own GPIO pin mostly. Since the Arduino doesn't have 50 GPIO pins, especially not for analog input, you need to have external IC(s), ADCs (Analog Digital Converters) or analog multiplexers, see also connecting more than 6 analog input pins to Arduino.

One wire sensors (your case)

You might find how many ds18b20 temperature sensors can I connect to one bus interesting.