Another change in working habits was the fact that young children began working along with adults in textile mills. Since the repetitive tasks they did there were considered easy, they could be paid less. In 1841, the British census found that the three most common occupations for boys were agricultural laborer, domestic servant and cotton manufacturer -- the latter two driven by the need of the new middle class for servants, and of the mills for cheap labor. In the burgeoning coal mines providing the fuel that fed the steam engines, a third of the workers were boys and girls under the age of 18.
The first successful bi-directional transmission of clear speech by Bell and Watson was made on March 10, 1876, when Bell spoke into the device, "Mr. Watson, come here, I want to see you." and Watson answered. Bell tested Gray's liquid transmitter design  in this experiment, but only after Bell's patent was granted and only as a proof of concept scientific experiment  to prove to his own satisfaction that intelligible "articulate speech" (Bell's words) could be electrically transmitted.  Because a liquid transmitter was not practical for commercial products, Bell focused on improving the electromagnetic telephone after March 1876 and never used Gray's liquid transmitter in public demonstrations or commercial use.